Method and user equipment for receiving downlink signals, and method and base station for transmitting downlink signals

ABSTRACT

Provided are methods and devices for transmitting/receiving downlink signals in a Wireless communication system. Carrier information is provided to user equipment, the carrier information including cell identifier information which indicates Whether a first cell identifier related to a first carrier operating on one resource block (RB) and a second cell identifier used for a cell-specific reference signal (CRS) on the first carrier are the same or different. If the second cell identifier is the same as the first cell identifier, the user equipment assumes that the number of antenna ports for the CRS on the first carrier is the same as the number of antenna ports for a reference signal defined for NB-IoT (reference signal for NB-IoT, NRS). If the second cell identifier is different from the first cell identifier, the carrier information further includes antenna port number information, and the user equipment assumes that the number of the antenna ports for the CRS is the same as the number of antenna ports based on the antenna port number information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/765,717, filed on Apr. 3, 2018, now U.S. Pat. No. 10,505,778, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2016/011607, filed on Oct. 17, 2016, which claimsthe benefit of U.S. Provisional Application No. 62/243,644, filed onOct. 19, 2015, and 62/335,644, filed on May 12, 2016, the contents ofwhich are all hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting or receiving downlinkcontrol and an apparatus therefor.

BACKGROUND ART

With appearance and spread of machine-to-machine (M2M) communication anda variety of devices such as smartphones and tablet PCs and technologydemanding a large amount of data transmission, data throughput needed ina cellular network has rapidly increased. To satisfy such rapidlyincreasing data throughput, carrier aggregation technology, cognitiveradio technology, etc. for efficiently employing more frequency bandsand multiple input multiple output (MIMO) technology, multi-base station(BS) cooperation technology, etc. for raising data capacity transmittedon limited frequency resources have been developed.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). A base station (BS) and a userequipment (UE) transmit and receive data and/or control informationscheduled on a prescribed time unit basis, e.g. on a subframe basis. Thedata is transmitted and received through a data region configured in aUL/DL subframe and the control information is transmitted and receivedthrough a control region configured in the UL/DL subframe. To this end,various physical channels carrying radio signals are formed in the UL/DLsubframe. In contrast, carrier aggregation technology serves to use awider UL/DL bandwidth by aggregating a plurality of UL/DL frequencyblocks in order to use a broader frequency band so that more signalsrelative to signals when a single carrier is used can be simultaneouslyprocessed.

In addition, a communication environment has evolved into increasingdensity of nodes accessible by a user at the periphery of the nodes. Anode refers to a fixed point capable of transmitting/receiving a radiosignal to/from the UE through one or more antennas. A communicationsystem including high-density nodes may provide a better communicationservice to the UE through cooperation between the nodes.

DISCLOSURE Technical Problem

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

A base station may provide a user equipment with carrier informationincluding identifier information indicating whether a second cellidentifier used for a cell-specific reference signal (CRS) on a firstcarrier is the same as or different from a first cell identifier. If thesecond cell identifier is the same as the first cell identifier, theuser equipment may assume that the number of antenna ports for the CRSon the first carrier is the same as the number of antenna ports for areference signal for NB-IoT (NRS). If the second cell identifier isdifferent from the first cell identifier, the carrier information mayfurther include number-of-antenna ports information. If the second cellidentifier is different from the first cell identifier, the userequipment may assume that the number of antenna ports for the CRS is thesame as the number of antenna ports corresponding to thenumber-of-antenna ports information.

According to an aspect of the present invention, provided herein is amethod of receiving a downlink signal in narrowband Internet of things(NB-IoT) by a user equipment in a wireless communication system. Themethod may include acquiring a first cell identifier; receiving carrierinformation including cell identifier information indicating whether asecond cell identifier used for a cell-specific reference signal (CRS)is the same as or different from the first cell identifier; andreceiving the downlink signal on a first carrier based on the cellidentifier information. The first carrier may operate in one resourceblock (RB). If the second cell identifier is the same as the first cellidentifier, the downlink signal may be received on the first carrierunder the assumption that the number of antenna ports for the CRS is thesame as the number of antenna ports for a reference signal for theNB-IoT (NRS). If the second cell identifier is different from the firstcell identifier, the carrier information may further includenumber-of-antenna ports information and the downlink signal may bereceived on the first carrier under the assumption that the number ofantenna ports for the CRS is the same as the number of antenna portscorresponding to the number-of-antenna ports information.

According to another aspect of the present invention, provided herein isa method of transmitting a downlink signal in narrowband Internet ofthings (NB-IoT) by a bases station in a wireless communication system.The method may include transmitting information indicating a first cellidentifier; transmitting carrier information including cell identifierinformation indicating whether a second cell identifier used for acell-specific reference signal (CRS) is the same as or different fromthe first cell identifier; and transmitting the downlink signal and theCRS on a first carrier based on the cell identifier information. Thefirst carrier may operate in one resource block (RB). If the second cellidentifier is the same as the first cell identifier, the CRS may betransmitted on the first carrier through antenna ports of the samenumber as the number of antenna ports for a reference signal for theNB-IoT (NRS). If the second cell identifier is different from the firstcell identifier, the carrier information may further includenumber-of-antenna ports information and the CRS may be transmitted onthe first carrier through antenna ports of a number corresponding to thenumber-of-antenna ports information.

According to another aspect of the present invention, provided herein isa user equipment for receiving a downlink signal in narrowband Internetof things (NB-IoT) in a wireless communication system. The userequipment may include a radio frequency (RF) unit, and a processorconfigured to control the RF unit. The processor may be configured to:acquire a first cell identifier; control the RF unit to receive carrierinformation including cell identifier information indicating whether asecond cell identifier used for a cell-specific reference signal (CRS)is the same as or different from the first cell identifier; and controlthe RF unit to receive the downlink signal on a first carrier based onthe cell identifier information. The first carrier may operate in oneresource block (RB). If the second cell identifier is the same as thefirst cell identifier, the processor may control the RF unit to receivethe downlink signal on the first carrier under the assumption that thenumber of antenna ports for the CRS is the same as the number of antennaports for a reference signal for the NB-IoT (NRS). If the second cellidentifier is different from the first cell identifier, the carrierinformation may further include number-of-antenna ports information. Ifthe second cell identifier is different from the first cell identifier,the processor may control the RF unit to receive the downlink signal onthe first carrier under the assumption that the number of antenna portsfor the CRS is the same as the number of antenna ports corresponding tothe number-of-antenna ports information.

According to another aspect of the present invention, provided herein isa base station for transmitting a downlink signal in narrowband Internetof things (NB-IoT) in a wireless communication system. The base stationmay include a radio frequency (RF) unit, and a processor configured tocontrol the RF unit. The processor may be configured to: control the RFunit to transmit information indicating a first cell identifier; controlthe RF unit to transmit carrier information including cell identifierinformation indicating whether a second cell identifier used for acell-specific reference signal (CRS) is the same as or different fromthe first cell identifier; and control the RF unit to transmit thedownlink signal and the CRS on a first carrier based on the cellidentifier information. The first carrier may operate in one resourceblock (RB). If the second cell identifier is the same as the first cellidentifier, the processor may control the RF unit to transmit the CRS onthe first carrier through antenna ports of the same number as the numberof antenna ports for a reference signal for the NB-IoT (NRS). If thesecond cell identifier is different from the first cell identifier, thecarrier information may further include number-of-antenna portsinformation. If the second cell identifier is different from the firstcell identifier, the processor may control the RF unit to transmit theCRS on the first carrier through antenna ports of a number correspondingto the number-of-antenna ports information.

In each aspect of the present invention, the one RB in which the firstcarrier operates may be an RB within a channel band used in the wirelesscommunication system.

In each aspect of the present invention, a frequency location of the CRSmay be determined based on the first cell identifier.

In each aspect of the present invention, the carrier information mayfurther include information indicating the number of orthogonalfrequency division multiplexing (OFDM) symbols for a downlink controlchannel on the first carrier.

In each aspect of the present invention, the carrier information may betransmitted on a second carrier different from the first carrier. Thesecond carrier may be a carrier with an NB-IoT synchronization signal(nSS) and an NB-IoT physical broadcast channel (nPBCH) and the firstcarrier may be a carrier without the nSS and the nPBCH.

In each aspect of the present invention, the second carrier may be acarrier operating in one RB within a guard band used in the wirelesscommunication system.

In each aspect of the present invention, the base station may transmitthe downlink signal through rate-matching on a CRS resourcecorresponding to the number of antenna ports for the CRS. The userequipment may receive or decode the downlink signal under the assumptionthat the downlink signal is transmitted through rate-matching.

The above technical solutions are merely some parts of the embodimentsof the present invention and various embodiments into which thetechnical features of the present invention are incorporated can bederived and understood by persons skilled in the art from the followingdetailed description of the present invention.

Advantageous Effect

According to the present invention, uplink/downlink signals can beefficiently transmitted/received. Therefore, overall throughput of awireless communication system is improved.

According to an embodiment of the present invention, alow-complexity/low-cost UE can communicate with a BS while maintainingcompatibility with a legacy system.

According to an embodiment of the present invention, a UE can beimplemented with low complexity/low cost.

According to an embodiment of the present invention, a UE and an eNB cancommunicate in a narrowband.

According to an embodiment of the present invention, small amounts ofdata can be efficiently transmitted/received.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot ina wireless communication system.

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS).

FIG. 4 illustrates the structure of a DL subframe used in a wirelesscommunication system.

FIG. 5 illustrates a cell-specific reference signal (CRS) and aUE-specific reference signal (UE-RS).

FIG. 6 illustrates the structure of a UL subframe used in a wirelesscommunication system.

FIG. 7 illustrates an exemplary signal band for MTC.

FIGS. 8 to 11 are diagrams illustrating synchronization signal carriercandidates according to the present invention.

FIG. 12 is a diagram illustrating a status and transition for a UEaccording to the present invention.

FIG. 13 illustrates a relationship between a (legacy) CRS and an in-bandIoT carrier according to the present invention.

FIG. 14 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

MODE FOR INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmitting device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmitting devices always sense carrier of a networkand, if the network is empty, the transmitting devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmitting devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmitting device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmittingdevice using a specific rule.

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port, avirtual antenna, or an antenna group. A node may be referred to as apoint.

In the present invention, a cell refers to a prescribed geographicregion to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell. Furthermore, channelstatus/quality of a specific cell refers to channel status/quality of achannel or communication link formed between an eNB or node whichprovides a communication service to the specific cell and a UE. In aLTE/LTE-A based system, The UE may measure DL channel state receivedfrom a specific node using cell-specific reference signal(s) (CRS(s))transmitted on a CRS resource allocated by antenna port(s) of thespecific node to the specific node and/or channel state informationreference signal(s) (CSI-RS(s)) transmitted on a CSI-RS resource. For adetailed CSI-RS configuration, refer to documents such as 3GPP TS 36.211and 3GPP TS 36.331.

Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a cell to managea radio resource. A cell associated with the radio resource is differentfrom a cell of a geographic region.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide a service using a carrier and a “cell” of aradio resource is associated with bandwidth (BW) which is a frequencyrange configured by the carrier. Since DL coverage, which is a rangewithin which the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, coverage of the node may be associated with coverage of “cell”of a radio resource used by the node. Accordingly, the term “cell” maybe used to indicate service coverage by the node sometimes, a radioresource at other times, or a range that a signal using a radio resourcecan reach with valid strength at other times. The “cell” of the radioresource will be described later in more detail.

3GPP LTE/LTE-A standards define DL physical channels corresponding toresource elements carrying information derived from a higher layer andDL physical signals corresponding to resource elements which are used bya physical layer but which do not carry information derived from ahigher layer. For example, a physical downlink shared channel (PDSCH), aphysical broadcast channel (PBCH), a physical multicast channel (PMCH),a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid ARQ indicatorchannel (PHICH) are defined as the DL physical channels, and a referencesignal and a synchronization signal are defined as the DL physicalsignals. A reference signal (RS), also called a pilot, refers to aspecial waveform of a predefined signal known to both a BS and a UE. Forexample, a cell-specific RS (CRS), a UE-specific RS (UE-RS), apositioning RS (PRS), and channel state information RS (CSI-RS) may bedefined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A standards define ULphysical channels corresponding to resource elements carryinginformation derived from a higher layer and UL physical signalscorresponding to resource elements which are used by a physical layerbut which do not carry information derived from a higher layer. Forexample, a physical uplink shared channel (PUSCH), a physical uplinkcontrol channel (PUCCH), and a physical random access channel (PRACH)are defined as the UL physical channels, and a demodulation referencesignal (DMRS) for a UL control/data signal and a sounding referencesignal (SRS) used for UL channel measurement are defined as the ULphysical signal.

In the present invention, a physical downlink control channel (PDCCH), aphysical control format indicator channel (PCFICH), a physical hybridautomatic retransmit request indicator channel (PHICH), and a physicaldownlink shared channel (PDSCH) refer to a set of time-frequencyresources or resource elements (REs) carrying downlink controlinformation (DCI), a set of time-frequency resources or REs carrying acontrol format indicator (CFI), a set of time-frequency resources or REscarrying downlink acknowledgement (ACK)/negative ACK (NACK), and a setof time-frequency resources or REs carrying downlink data, respectively.In addition, a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a physical random access channel(PRACH) refer to a set of time-frequency resources or REs carryinguplink control information (UCI), a set of time-frequency resources orREs carrying uplink data and a set of time-frequency resources or REscarrying random access signals, respectively. In the present invention,in particular, a time-frequency resource or RE that is assigned to orbelongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to asPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,respectively. Therefore, in the present invention, PUCCH/PUSCH/PRACHtransmission of a UE is conceptually identical to UCI/uplink data/randomaccess signal transmission on PUSCH/PUCCH/PRACH, respectively. Inaddition, PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB isconceptually identical to downlink data/DCI transmission onPDCCH/PCFICH/PHICH/PDSCH, respectively.

Hereinafter, OFDM symbol/subcarrier/RE to or for whichCRS/DMRS/CSI-RS/SRS/UE-RS is assigned or configured will be referred toas CRS/DMRS/CSI-RS/SRS/UE-RS symbol/carrier/subcarrier/RE. For example,an OFDM symbol to or for which a tracking RS (TRS) is assigned orconfigured is referred to as a TRS symbol, a subcarrier to or for whichthe TRS is assigned or configured is referred to as a TRS subcarrier,and an RE to or for which the TRS is assigned or configured is referredto as a TRS RE. In addition, a subframe configured for transmission ofthe TRS is referred to as a TRS subframe. Moreover, a subframe in whicha broadcast signal is transmitted is referred to as a broadcast subframeor a PBCH subframe and a subframe in which a synchronization signal(e.g. PSS and/or SSS) is transmitted is referred to a synchronizationsignal subframe or a PSS/SSS subframe. OFDM symbol/subcarrier/RE to orfor which PSS/SSS is assigned or configured is referred to as PSS/SSSsymbol/subcarrier/RE, respectively.

In the present invention, a CRS port, a UE-RS port, a CSI-RS port, and aTRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna ports configured to transmit CRSs may bedistinguished from each other by the locations of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the locations of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the locationsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a patternof REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a predetermined resourceregion.

For terms and technologies which are not described in detail in thepresent invention, reference can be made to standard documents of 3GPPLTE/LTE-A, for example, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS 36.213,3GPP TS 36.321, and 3GPP TS 36.331.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

Specifically, FIG. 1(a) illustrates an exemplary structure of a radioframe which can be used in frequency division multiplexing (FDD) in 3GPPLTE/LTE-A and FIG. 1(b) illustrates an exemplary structure of a radioframe which can be used in time division multiplexing (TDD) in 3GPPLTE/LTE-A. The frame structure of FIG. 1(a) is referred to as framestructure type 1 (FS1) and the frame structure of FIG. 1(b) is referredto as frame structure type 2 (FS2).

Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms(307,200T_(s)) in duration. The radio frame is divided into 10 subframesof equal size. Subframe numbers may be assigned to the 10 subframeswithin one radio frame, respectively. Here, T_(s) denotes sampling timewhere T_(s)=1/(2048*15 kHz). Each subframe is 1 ms long and is furtherdivided into two slots. 20 slots are sequentially numbered from 0 to 19in one radio frame. Duration of each slot is 0.5 ms. A time interval inwhich one subframe is transmitted is defined as a transmission timeinterval (TTI). Time resources may be distinguished by a radio framenumber (or radio frame index), a subframe number (or subframe index), aslot number (or slot index), and the like.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

Table 1 shows an exemplary UL-DL configuration within a radio frame inTDD mode.

TABLE 1 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

In Table 1, D denotes a DL subframe, U denotes a UL subframe, and Sdenotes a special subframe. The special subframe includes three fields,i.e. downlink pilot time slot (DwPTS), guard period (GP), and uplinkpilot time slot (UpPTS). DwPTS is a time slot reserved for DLtransmission and UpPTS is a time slot reserved for UL transmission.Table 2 shows an example of the special subframe configuration.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix in downUpPTS UpPTS Special Normal Extended Normal Extended subframe cyclicprefix cyclic prefix cyclic prefix cyclic prefix configuration DwPTS inuplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192 · T_(s)2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 · T_(s)20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600 ·T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592 ·T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) — 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

FIG. 2 illustrates the structure of a DL/UL slot structure in a wirelesscommunication system. In particular, FIG. 2 illustrates the structure ofa resource grid of a 3GPP LTE/LTE-A system. One resource grid is definedper antenna port.

Referring to FIG. 2, a slot includes a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. The OFDMsymbol may refer to one symbol duration. Referring to FIG. 2, a signaltransmitted in each slot may be expressed by a resource grid includingN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. N^(DL) _(RB) denotes the number of RBs in a DL slot and N^(UL)_(RB) denotes the number of RBs in a UL slot. N^(DL) _(RB) and N^(UL)_(RB) depend on a DL transmission bandwidth and a UL transmissionbandwidth, respectively. N^(DL) _(symb) denotes the number of OFDMsymbols in a DL slot, N^(UL) _(symb) denotes the number of OFDM symbolsin a UL slot, and N^(RB) _(sc) denotes the number of subcarriersconfiguring one RB.

An OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access schemes. The number of OFDM symbols included in one slotmay be varied according to channel bandwidths and CP lengths. Forexample, in a normal cyclic prefix (CP) case, one slot includes 7 OFDMsymbols. In an extended CP case, one slot includes 6 OFDM symbols.Although one slot of a subframe including 7 OFDM symbols is shown inFIG. 2 for convenience of description, embodiments of the presentinvention are similarly applicable to subframes having a differentnumber of OFDM symbols. Referring to FIG. 2, each OFDM symbol includesN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers in the frequency domain. Thetype of the subcarrier may be divided into a data subcarrier for datatransmission, a reference signal (RS) subcarrier for RS transmission,and a null subcarrier for a guard band and a DC component. The nullsubcarrier for the DC component is unused and is mapped to a carrierfrequency f₀ in a process of generating an OFDM signal or in a frequencyup-conversion process. The carrier frequency is also called a centerfrequency f_(c).

One RB is defined as N^(DL/UL) _(symb) (e.g. 7) consecutive OFDM symbolsin the time domain and as N^(RB) _(sc) (e.g. 12) consecutive subcarriersin the frequency domain. For reference, a resource composed of one OFDMsymbol and one subcarrier is referred to a resource element (RE) ortone. Accordingly, one RB includes N^(DL/UL) _(symb)*N^(RB) _(sc) REs.Each RE within a resource grid may be uniquely defined by an index pair(k, l) within one slot. k is an index ranging from 0 to N^(DL/UL)_(RB)*N^(RB) _(sc)−1 in the frequency domain, and l is an index rangingfrom 0 to N^(DL/UL) _(symb)1−1 in the time domain.

Meanwhile, one RB is mapped to one physical resource block (PRB) and onevirtual resource block (VRB). A PRB is defined as N^(DL) _(symb) (e.g.7) consecutive OFDM or SC-FDM symbols in the time domain and N^(RB)_(sc) (e.g. 12) consecutive subcarriers in the frequency domain.Accordingly, one PRB is configured with N^(DL/UL) _(symb)*N^(RB) _(sc)REs. In one subframe, two RBs each located in two slots of the subframewhile occupying the same N^(RB) _(sc) consecutive subcarriers arereferred to as a physical resource block (PRB) pair. Two RBs configuringa PRB pair have the same PRB number (or the same PRB index).

FIG. 3 illustrates a radio frame structure for transmission of asynchronization signal (SS). Specifically, FIG. 3 illustrates a radioframe structure for transmission of an SS and a PBCH in frequencydivision duplex (FDD), wherein FIG. 3(a) illustrates transmissionlocations of an SS and a PBCH in a radio frame configured as a normalcyclic prefix (CP) and FIG. 3(b) illustrates transmission locations ofan SS and a PBCH in a radio frame configured as an extended CP.

If a UE is powered on or newly enters a cell, the UE performs an initialcell search procedure of acquiring time and frequency synchronizationwith the cell and detecting a physical cell identity N^(cell) _(ID) ofthe cell. To this end, the UE may establish synchronization with the eNBby receiving synchronization signals, e.g. a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS), from the eNBand obtain information such as a cell identity (ID).

An SS will be described in more detail with reference to FIG. 3. An SSis categorized into a PSS and an SSS. The PSS is used to acquiretime-domain synchronization of OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization and theSSS is used to acquire frame synchronization, a cell group ID, and/or CPconfiguration of a cell (i.e. information as to whether a normal CP isused or an extended CP is used). Referring to FIG. 3, each of a PSS andan SSS is transmitted on two OFDM symbols of every radio frame. Morespecifically, SSs are transmitted in the first slot of subframe 0 andthe first slot of subframe 5, in consideration of a global system formobile communication (GSM) frame length of 4.6 ms for facilitation ofinter-radio access technology (inter-RAT) measurement. Especially, a PSSis transmitted on the last OFDM symbol of the first slot of subframe 0and on the last OFDM symbol of the first slot of subframe 5 and an SSSis transmitted on the second to last OFDM symbol of the first slot ofsubframe 0 and on the second to last OFDM symbol of the first slot ofsubframe 5. A boundary of a corresponding radio frame may be detectedthrough the SSS. The PSS is transmitted on the last OFDM symbol of acorresponding slot and the SSS is transmitted on an OFDM symbolimmediately before an OFDM symbol on which the PSS is transmitted. Atransmit diversity scheme of an SS uses only a single antenna port andstandards therefor are not separately defined.

Referring to FIG. 3, upon detecting a PSS, a UE may discern that acorresponding subframe is one of subframe 0 and subframe 5 because thePSS is transmitted every 5 ms but the UE cannot discern whether thesubframe is subframe 0 or subframe 5. Accordingly, the UE cannotrecognize the boundary of a radio frame only by the PSS. That is, framesynchronization cannot be acquired only by the PSS. The UE detects theboundary of a radio frame by detecting an SSS which is transmitted twicein one radio frame with different sequences.

A UE, which has demodulated a DL signal by performing a cell searchprocedure using an SSS and determined time and frequency parametersnecessary for transmitting a UL signal at an accurate time, cancommunicate with an eNB only after acquiring system informationnecessary for system configuration of the UE from the eNB.

The system information is configured by a master information block (MIB)and system information blocks (SIBs). Each SIB includes a set offunctionally associated parameters and may be categorized into an MIB,SIB Type 1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB17 according toincluded parameters.

The MIB includes most frequency transmitted parameters which areessential for initial access of the UE to a network of the eNB. The UEmay receive the MIB through a broadcast channel (e.g. a PBCH). The MIBincludes DL bandwidth (BW), PHICH configuration, and a system framenumber SFN. Accordingly, the UE can be explicitly aware of informationabout the DL BW, SFN, and PHICH configuration by receiving the PBCH.Meanwhile, information which can be implicitly recognized by the UEthrough reception of the PBCH is the number of transmit antenna ports ofthe eNB. Information about the number of transmit antennas of the eNB isimplicitly signaled by masking (e.g. XOR operation) a sequencecorresponding to the number of transmit antennas to a 16-bit cyclicredundancy check (CRC) used for error detection of the PBCH.

SIB1 includes not only information about time-domain scheduling of otherSIBs but also parameters needed to determine whether a specific cell issuitable for cell selection. SIB1 is received by the UE throughbroadcast signaling or dedicated signaling.

A DL carrier frequency and a system BW corresponding to the DL carrierfrequency may be acquired by the MIB that the PBCH carries. A UL carrierfrequency and a system BW corresponding to the UL carrier frequency maybe acquired through system information which is a DL signal. If nostored valid system information about a corresponding cell is present asa result of receiving the MIB, the UE applies a DL BW in the MIB to a ULBW until SIB2 is received. For example, the UE may recognize an entireUL system BW which is usable for UL transmission thereby throughUL-carrier frequency and UL-BW information in SIB2 by acquiring SIB2.

In the frequency domain, a PSS/SSS and a PBCH are transmitted only in atotal of 6 RBs, i.e. a total of 72 subcarriers, irrespective of actualsystem BW, wherein 3 RBs are in the left and the other 3 RBs are in theright centering on a DC subcarrier on corresponding OFDM symbols.Therefore, the UE is configured to detect or decode the SS and the PBCHirrespective of DL BW configured for the UE.

After initial cell search, the UE may perform a random access procedureto complete access to the eNB. To this end, the UE may transmit apreamble through a physical random access channel (PRACH) and receive aresponse message to the preamble through a PDCCH and a PDSCH. Incontention based random access, the UE may perform additional PRACHtransmission and a contention resolution procedure of a PDCCH and aPDSCH corresponding to the PDCCH.

After performing the aforementioned procedure, the UE may performPDCCH/PDSCH reception and PUSCH/PUCCH transmission as generaluplink/downlink transmission procedures.

The random access procedure is also referred to as a random accesschannel (RACH) procedure. The random access procedure is used forvarious purposes including initial access, adjustment of ULsynchronization, resource assignment, and handover. Random accessprocedures are categorized into a contention-based procedure and adedicated (i.e., non-contention-based) procedure. The contention-basedrandom access procedure is used for general operations including initialaccess, while the dedicated random access procedure is used for limitedoperations such as handover. In the contention-based random accessprocedure, the UE randomly selects a RACH preamble sequence.Accordingly, it is possible for multiple UEs to transmit the same RACHpreamble sequence at the same time. Thereby, a contention resolutionprocedure needs to be subsequently performed. On the other hand, in thededicated random access procedure, the UE uses an RACH preamble sequencethat the eNB uniquely allocates to the UE. Accordingly, the randomaccess procedure may be performed without collision with other UEs.

The contention-based random access procedure includes the following foursteps. Messages transmitted in Steps 1 to 4 given below may be referredto as Msg1 to Msg4.

Step 1: RACH preamble (via PRACH) (from UE to eNB)

Step 2: Random access response (RAR) (via PDCCH and PDSCH) (from eNB toUE)

Step 3: Layer 2/layer 3 message (via PUSCH) (from UE to eNB)

Step 4: Contention resolution message (from eNB to UE)

The dedicated random access procedure includes the following threesteps. Messages transmitted in Steps 0 to 2 may be referred to as Msg0to Msg2, respectively. Uplink transmission (i.e., Step 3) correspondingto the RAR may also be performed as a part of the random accessprocedure. The dedicated random access procedure may be triggered usinga PDCCH for ordering transmission of an RACH preamble (hereinafter, aPDCCH order).

Step 0: RACH preamble assignment (from eNB to UE) through dedicatedsignaling

Step 1: RACH preamble (via PRACH) (from UE to eNB)

Step 2: RAR (via PDCCH and PDSCH) (from eNB to UE)

After transmitting the RACH preamble, the UE attempts to receive an RARwithin a preset time window. Specifically, the UE attempts to detect aPDCCH with RA-RNTI (Random Access RNTI) (hereinafter, RA-RNTI PDCCH)(e.g., CRC is masked with RA-RNTI on the PDCCH) in the time window. Indetecting the RA-RNTI PDCCH, the UE checks the PDSCH for presence of anRAR directed thereto. The RAR includes timing advance (TA) informationindicating timing offset information for UL synchronization, UL resourceallocation information (UL grant information), and a temporary UEidentifier (e.g., temporary cell-RNTI (TC-RNTI)). The UE may perform ULtransmission (of, e.g., Msg3) according to the resource allocationinformation and the TA value in the RAR. HARQ is applied to ULtransmission corresponding to the RAR. Accordingly, after transmittingMsg3, the UE may receive acknowledgement information (e.g., PHICH)corresponding to Msg3.

FIG. 4 illustrates the structure of a DL subframe used in a wirelesscommunication system.

Referring to FIG. 4, a DL subframe is divided into a control region anda data region in the time domain. Referring to FIG. 4, a maximum of 3(or 4) OFDM symbols located in a front part of a first slot of asubframe corresponds to the control region. Hereinafter, a resourceregion for PDCCH transmission in a DL subframe is referred to as a PDCCHregion. OFDM symbols other than the OFDM symbol(s) used in the controlregion correspond to the data region to which a physical downlink sharedchannel (PDSCH) is allocated. Hereinafter, a resource region availablefor PDSCH transmission in the DL subframe is referred to as a PDSCHregion.

Examples of a DL control channel used in 3GPP LTE include a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc.

The PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols available fortransmission of a control channel within a subframe. The PCFICH notifiesthe UE of the number of OFDM symbols used for the corresponding subframeevery subframe. The PCFICH is located at the first OFDM symbol. ThePCFICH is configured by four resource element groups (REGs), each ofwhich is distributed within a control region on the basis of cell ID.One REG includes four REs.

A set of OFDM symbols available for the PDCCH at a subframe is given bythe following Table.

TABLE 3 Number of OFDM Number of OFDM symbols for PDCCH symbols forPDCCH Subframe when N^(DL) _(RB) > 10 when N^(DL) _(RB) ≤ 10 Subframe 1and 6 for 1, 2 2 frame structure type 2 MBSFN subframes on a 1, 2 2carrier supporting PDSCH, configured with 1 or 2 cell-specific antennaports MBSFN subframes on a 2 2 carrier supporting PDSCH, configured with4 cell- specific antenna ports Subframes on a carrier 0 0 not supportingPDSCH Non-MBSFN subframes 1, 2, 3 2, 3 (except subframe 6 for framestructure type 2) configured with positioning reference signals Allother cases 1, 2, 3 2, 3, 4

A subset of downlink subframes within a radio frame on a carrier forsupporting PDSCH transmission may be configured as MBSFN subframe(s) bya higher layer. Each MBSFN subframe is divided into a non-MBSFN regionand an MBSFN region. The non-MBSFN region spans first one or two OFDMsymbols, and its length is given by Table 3. The same CP as cyclicprefix (CP) used for subframe 0 is used for transmission within thenon-MBSFN region of the MBSFN subframe. The MBSFN region within theMBSFN subframe is defined as OFDM symbols which are not used in thenon-MBSFN region.

The PCFICH carries a control format indicator (CFI), which indicates anyone of values of 1 to 3. For a downlink system bandwidth N^(DL)_(RB)>10, the number 1, 2 or 3 of OFDM symbols which are spans of DCIcarried by the PDCCH is given by the CFI. For a downlink systembandwidth N^(DL) _(RB)≤10, the number 2, 3 or 4 of OFDM symbols whichare spans of DCI carried by the PDCCH is given by CFI+1. The CFI iscoded in accordance with the following Table.

TABLE 4 CFI code word CFI <b₀, b₁, . . . , b₃₁> 1 <0, 1, 1, 0, 1, 1, 0,1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0,1> 2 <1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,0, 1, 1, 0, 1, 1, 0, 1, 1, 0> 3 <1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1> 4 <0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, (Reserved) 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0>

The PHICH carries a HARQ (Hybrid Automatic Repeat Request) ACK/NACK(acknowledgment/negative-acknowledgment) signal as a response to ULtransmission. The PHICH includes three REGs, and is scrambledcell-specifically. ACK/NACK is indicated by 1 bit, and the ACK/NACK of 1bit is repeated three times. Each of the repeated ACK/NACK bits isspread with a spreading factor (SF) 4 or 2 and then mapped into acontrol region.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a UE or UE group and other controlinformation. Transmit format and resource allocation information of adownlink shared channel (DL-SCH) are referred to as DL schedulinginformation or DL grant. Transmit format and resource allocationinformation of an uplink shared channel (UL-SCH) are referred to as ULscheduling information or UL grant. The size and usage of the DCIcarried by one PDCCH are varied depending on DCI formats. The size ofthe DCI may be varied depending on a coding rate. In the current 3GPPLTE system, various formats are defined, wherein formats 0 and 4 aredefined for a UL, and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3Aare defined for a DL. Combination selected from control information suchas a hopping flag, RB allocation, modulation coding scheme (MCS),redundancy version (RV), new data indicator (NDI), transmit powercontrol (TPC), cyclic shift, cyclic shift demodulation reference signal(DMRS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI) information istransmitted to the UE as the DCI.

A plurality of PDCCHs may be transmitted within a control region. A UEmay monitor the plurality of PDCCHs. An eNB determines a DCI formatdepending on the DCI to be transmitted to the UE, and attaches cyclicredundancy check (CRC) to the DCI. The CRC is masked (or scrambled) withan identifier (for example, a radio network temporary identifier (RNTI))depending on usage of the PDCCH or owner of the PDCCH. For example, ifthe PDCCH is for a specific UE, the CRC may be masked with an identifier(for example, cell-RNTI (C-RNTI)) of the corresponding UE. If the PDCCHis for a paging message, the CRC may be masked with a paging identifier(for example, paging-RNTI (P-RNTI)). If the PDCCH is for systeminformation (in more detail, system information block (SIB)), the CRCmay be masked with system information RNTI (SI-RNTI). If the PDCCH isfor a random access response, the CRC may be masked with a random accessRNTI (RA-RNTI). For example, CRC masking (or scrambling) includes XORoperation of CRC and RNTI at the bit level.

Generally, a DCI format, which may be transmitted to the UE, is varieddepending on a transmission mode configured for the UE. In other words,certain DCI format(s) corresponding to the specific transmission modenot all DCI formats may only be used for the UE configured to a specifictransmission mode.

For example, a transmission mode is semi-statically configured for theUE by a higher layer so that the UE may receive a PDSCH transmitted inaccordance with one of a plurality of transmission modes which arepreviously defined. The UE attempts to decode a PDCCH using DCI formatsonly corresponding to its transmission mode. In other words, in order tomaintain UE operation load according to blind decoding attempt, at acertain level or less, all DCI formats are not searched by the UE at thesame time.

Table 5 illustrates transmission modes for configuring multi-antennatechnology and DCI formats for allowing a UE to perform blind decodingat the corresponding transmission mode. Particularly, Table 5illustrates a relation between PDCCH and PDSCH configured by C-RNTI(Cell RNTI(Radio Network Temporary Identifier)).

TABLE 5 Transmission Transmission scheme of PDSCH mode DCI format SearchSpace corresponding to PDCCH Mode 1 DCI format 1A Common andSingle-antenna port, port 0 UE specific by C-RNTI DCI format 1 UEspecific by C-RNTI Single-antenna port, port 0 Mode 2 DCI format 1ACommon and Transmit diversity UE specific by C-RNTI DCI format 1 UEspecific by C-RNTI Transmit diversity Mode 3 DCI format 1A Common andTransmit diversity UE specific by C-RNTI DCI format 2A UE specific byC-RNTI Large delay CDD or Transmit diversity Mode 4 DCI format 1A Commonand Transmit diversity UE specific by C-RNTI DCI format 2 UE specific byC-RNTI Closed-loop spatial multiplexing or Transmit diversity Mode 5 DCIformat 1A Common and Transmit diversity UE specific by C-RNTI DCI format1D UE specific by C-RNTI Multi-user MIMO Mode 6 DCI format 1A Common andTransmit diversity UE specific by C-RNTI DCI format 1B UE specific byC-RNTI Closed-loop spatial multiplexing using a single transmissionlayer Mode 7 DCI format 1A Common and If the number of PBCH antennaports UE specific by C-RNTI is one, Single-antenna port, port 0 is used,otherwise Transmit diversity DCI format 1 UE specific by C-RNTISingle-antenna port, port 5 Mode 8 DCI format 1A Common and If thenumber of PBCH antenna ports UE specific by C-RNTI is one,Single-antenna port, port 0 is used, otherwise Transmit diversity DCIformat 2B UE specific by C-RNTI Dual layer transmission, port 7 and 8 orsingle-antenna port, port 7 or 8 Mode 9 DCI format 1A Common andNon-MBSFN subframe: If the number UE specific by C-RNTI of PBCH antennaports is one, Single- antenna port, port 0 is used, otherwise Transmitdiversity. MBSFN subframe: Single-antenna port, port 7 DCI format 2C UEspecific by C-RNTI Up to 8 layer transmission, ports 7-14 orsingle-antenna port, port 7 or 8 Mode 10 DCI format 1A Common andNon-MBSFN subframe: If the number of UE specific by C-RNTI PBCH antennaports is one, Single- antenna port, port 0 is used, otherwise Transmitdiversity. MBSFN subframe: Single-antenna port, port 7 DCI format 2D UEspecific by C-RNTI Up to 8 layer transmission, ports 7-14 or singleantenna port, port 7 or 8

Although transmission modes 1 to 10 are listed in Table 5, othertransmission modes in addition to the transmission modes defined inTable 5 may be defined.

The PDCCH is allocated to first m number of OFDM symbol(s) within asubframe. In this case, m is an integer equal to or greater than 1, andis indicated by the PCFICH.

The PDCCH is transmitted on an aggregation of one or a plurality ofcontinuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide a coding rate based on the status of aradio channel to the PDCCH. The CCE corresponds to a plurality ofresource element groups (REGs). For example, one CCE corresponds to nineresource element groups (REGs), and one REG corresponds to four REs.Four QPSK symbols are mapped to each REG. A resource element (RE)occupied by the reference signal (RS) is not included in the REG.Accordingly, the number of REGs within given OFDM symbols is varieddepending on the presence of the RS. The REGs are also used for otherdownlink control channels (that is, PDFICH and PHICH).

Assuming that the number of REGs not allocated to the PCFICH or thePHICH is N_(REG), the number of available CCEs in a DL subframe forPDCCH(s) in a system is numbered from 0 to N_(CCE)-1, whereN_(CCE)=floor(N_(REG)/9).

A DCI format and the number of DCI bits are determined in accordancewith the number of CCEs. The CCEs are numbered and consecutively used.To simplify the decoding process, a PDCCH having a format including nCCEs may be initiated only on CCEs assigned numbers corresponding tomultiples of n. The number of CCEs used for transmission of a specificPDCCH is determined by a network or the eNB in accordance with channelstatus. For example, one CCE may be required for a PDCCH for a UE (forexample, adjacent to eNB) having a good downlink channel. However, incase of a PDCCH for a UE (for example, located near the cell edge)having a poor channel, eight CCEs may be required to obtain sufficientrobustness. Additionally, a power level of the PDCCH may be adjusted tocorrespond to a channel status.

In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH can belocated for each UE is defined. A set of CCEs on which the UE candiscover a PDCCH thereof is referred to as a PDCCH search space orsimply as a search space. An individual resource on which the PDCCH canbe transmitted in the search space is called a PDCCH candidate. A set ofPDCCH candidates that the UE is to monitor is defined as a search space.Herein, a search space S^((L)) _(k) in an aggregation level L∈{1,2,4,8}is defined by a set of candidates of the PDCCH. A search space may havea different size and a dedicated search space and a common search spaceare defined. The dedicated search space is a UE-specific search space(USS) and is configured for each individual UE. The common search space(CSS) is configured for a plurality of UEs.

An eNB transmits an actual PDCCH (DCI) on a PDCCH candidate in a searchspace and a UE monitors the search space to detect the PDCCH (DCI).Here, monitoring implies attempting to decode each PDCCH in thecorresponding SS according to all monitored DCI formats. The UE maydetect a PDCCH thereof by monitoring a plurality of PDCCHs. Basically,the UE does not know the location at which a PDCCH thereof istransmitted. Therefore, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having an IDthereof is detected and this process is referred to as blind detection(or blind decoding (BD)).

For example, it is assumed that a specific PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datatransmitted using a radio resource “B” (e.g. frequency location) andusing transport format information “C” (e.g. transport block size,modulation scheme, coding information, etc.) is transmitted in aspecific DL subframe. Then, the UE monitors the PDCCH using RNTIinformation thereof. The UE having the RNTI “A” receives the PDCCH andreceives the PDSCH indicated by “B” and “C” through information of thereceived PDCCH.

FIG. 5 illustrates a configuration of CRSs and UE-RSs. In particular,FIG. 5 shows REs occupied by the CRS(s) and UE-RS(s) on an RB pair of asubframe having a normal CP.

In an existing 3GPP system, since CRSs are used for both demodulationand measurement, the CRSs are transmitted in all DL subframes in a cellsupporting PDSCH transmission and are transmitted through all antennaports configured at an eNB.

Referring to FIG. 5, a CRS is transmitted through antenna port p=0, p=0,1, or p=0, 1, 2, 3 according to the number of antenna ports of atransmission node. The CRS is fixed to a predetermined pattern in asubframe regardless of a control region and a data region. A controlchannel is allocated to a resource on which the CRS is not allocated inthe control region and a data channel is allocated to a resource onwhich the CRS is not allocated in the data region.

A UE may measure CSI using the CRSs and demodulate a signal received ona PDSCH in a subframe including the CRSs. That is, the eNB transmits theCRSs at predetermined locations in each RB of all RBs and the UEperforms channel estimation based on the CRSs and detects the PDSCH. Forexample, the UE may measure a signal received on a CRS RE and detect aPDSCH signal from an RE to which the PDSCH is mapped using the measuredsignal and using the ratio of reception energy per CRS RE to receptionenergy per PDSCH mapped RE. However, when the PDSCH is transmitted basedon the CRSs, since the eNB should transmit the CRSs in all RBs,unnecessary RS overhead occurs. To solve such a problem, in a 3GPP LTE-Asystem, a UE-RS and a CSI-RS are further defined in addition to a CRS.The UE-RS is used for demodulation and the CSI-RS is used to derive CSI.The UE-RS is one type of a DRS. Since the UE-RS and the CRS are used fordemodulation, the UE-RS and the CRS may be regarded as demodulation RSsin terms of usage. Since the CSI-RS and the CRS are used for channelmeasurement or channel estimation, the CSI-RS and the CRS may beregarded as measurement RSs.

Referring to FIG. 5, UE-RSs are transmitted on antenna port(s) p=5, p=7,p=8 or p=7, 8, . . . , υ+6 for PDSCH transmission, where υ is the numberof layers used for the PDSCH transmission. UE-RSs are present and are avalid reference for PDSCH demodulation only if the PDSCH transmission isassociated with the corresponding antenna port. UE-RSs are transmittedonly on RBs to which the corresponding PDSCH is mapped. That is, theUE-RSs are configured to be transmitted only on RB(s) to which a PDSCHis mapped in a subframe in which the PDSCH is scheduled unlike CRSsconfigured to be transmitted in every subframe irrespective of whetherthe PDSCH is present. Accordingly, overhead of the RS may be loweredcompared to that of the CRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 5, in a PRB having frequency-domain index n_(PRB)assigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . .. , υ+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols α_(k,l) ^((p)) in a subframe according to thefollowing equation.α_(k,l) ^((p)) =w _(p)(l′)·r(3·l′·N _(RB) ^(max,DL)+3·n _(PRB)+m′)  Equation 1

where w_(p)(i), l′, m′ are given as follows.

$\begin{matrix}{\mspace{79mu}{{w_{p}(i)} = \left\{ \begin{matrix}{{\overset{\_}{w}}_{p}(i)} & {{\left( {m^{\prime} + n_{PRB}} \right){mod}\; 2} = 0} \\{{\overset{\_}{w}}_{p}\left( {3 - i} \right)} & {{\left( {m^{\prime} + n_{PRB}} \right){mod}\; 2} = 1}\end{matrix}\; \right.}} & {{Equation}\mspace{14mu} 2} \\{\mspace{79mu}{k = {{5m^{\prime}} + {N_{sc}^{RB}n_{PRB}} + k^{\prime}}}} & \; \\{\mspace{79mu}{k^{\prime} = \left\{ \begin{matrix}1 & {p \in \left\{ {7,8,11,13} \right\}} \\0 & {p \in \left\{ {9,10,12,14} \right\}}\end{matrix} \right.}} & \; \\{l = \left\{ \begin{matrix}{{l^{\prime}{mod}\; 2} + 2} & {{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\\; & {{{configuration}\mspace{14mu} 3},{4\mspace{14mu}{or}\mspace{14mu} 8}} \\\; & \left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right) \\{{l^{\prime}{mod}\; 2} + 2 + {3\left\lfloor {l^{\prime}/2} \right\rfloor}} & {{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}\mspace{14mu}{with}} \\\; & {{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7}} \\\; & \left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right) \\{{l^{\prime}{mod}\; 2} + 5} & {{if}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}}\end{matrix} \right.} & \; \\{l = \left\{ \begin{matrix}{0,1,2,3} & {{{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = {0\mspace{14mu}{and}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{special}\mspace{14mu}{subframe}}}\mspace{11mu}} \\\; & {{{with}\mspace{14mu}{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7}} \\\; & \left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right) \\{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = {0\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{special}}} \\\; & {{subframe}\mspace{14mu}{with}\mspace{14mu}{configuration}} \\\; & {1,2,6,{{or}\mspace{14mu} 7\mspace{14mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}} \\{2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = {1\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{special}}} \\\; & {{subframe}\mspace{14mu}{with}\mspace{14mu}{configuration}} \\\; & {1,2,6,{{or}\mspace{14mu} 7\mspace{14mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}}\end{matrix} \right.} & \; \\{\mspace{79mu}{{m^{\prime} = 0},1,2}} & \;\end{matrix}$

Herein, n_(s) is a slot number in a radio frame, which is one of theintegers of 0 to 19. The sequence w _(p)(i) for normal CP is givenaccording to the following equation.

TABLE 6 Antenna port p [w _(p)(0) w _(p)(1) w _(p)(2) w _(p)(3)] 7 [+1+1 +1 +1] 8 [+1 −1 +1 −1] 9 [+1 +1 +1 +1 10 [+1 −1 +1 −1] 11 [+1 +1 −1−1] 12 [−1 −1 +1 +1] 13 [+1 −1 −1 +1] 14 [−1 +1 +1 −1]

For antenna port p∈{7, 8, . . . , υ+6}, the UE-RS sequence r(m) isdefined as follows.

$\begin{matrix}{\mspace{79mu}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2\; m} + 1} \right)}}} \right)}}},}} & {{Equation}\mspace{14mu} 3} \\{m = \left\{ \begin{matrix}{0,1,\ldots\mspace{14mu},{{12N_{RB}^{\max,{DL}}} - 1}} & {{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}} \\{0,1,\ldots\mspace{14mu},{{16N_{RB}^{\max,{DL}}} - 1}} & {{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \right.} & \;\end{matrix}$

c(i) is a pseudo-random sequence defined by a length-31 Gold sequence.The output sequence c(n) of length M_(PN), where n=0, 1, . . . ,M_(PN)-1, is defined by the following equation.c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  Equation 4

where N_(C)=1600 and the first m-sequence is initialized with x₁(0)=1,x₁(n)=0, n=1, 2, . . . , 30. The initialization of the second m-sequenceis denoted by c_(init)=Σ_(i=0) ³⁰x₂(i)·2^(i) with the value depending onthe application of the sequence.

In Equation 3, the pseudo-random sequence generator for generating c(i)is initialized with c_(init) at the start of each subframe according tothe following equation.c _(init)=(└n _(s)/2┘+1)·(2n _(ID) ^((n) ^(SCID) ⁾+1)·2¹⁶ +n_(SCID)  Equation 5

In Equation 5, the quantities n^((i)) _(ID), i=0, 1, which iscorresponding to n_(ID) ^((n) ^(SCID) ⁾, is given by a physical layercell identifier N^(cell) _(ID) if no value for n^(DMRS,i) _(ID) isprovided by higher layers or if DCI format 1A, 2B or 2C is used for DCIformat associated with the PDSCH transmission, and given by n^(DMRS,i)_(ID) otherwise.

In Equation 5, the value of n_(SCID) is zero unless specified otherwise.For a PDSCH transmission on antenna ports 7 or 8, n_(SCID) is given bythe DCI format 2B or 2D. DCI format 2B is a DCI format for resourceassignment for a PDSCH using a maximum of two antenna ports havingUE-RSs. DCI format 2C is a DCI format for resource assignment for aPDSCH using a maximum of 8 antenna ports having UE-RSs.

An RS sequence r_(l,ns)(m) for a CRS is defined as follows.

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2\; m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2\; m} + 1} \right)}}} \right)}}},} & {{Equation}\mspace{14mu} 6} \\{{m = 0},1,\ldots\mspace{14mu},{{2N_{RB}^{\max,{DL}}} - 1}} & \;\end{matrix}$

Herein, N^(max,DL) _(RB) denotes the largest DL bandwidth configuration,represented as a multiple of N^(RB) _(sc). n_(s) denotes a slot numberin a radio frame and l denotes an OFDM symbol number in a slot. Apseudo-random sequence c(i) is defined by Equation 4. A pseudo-randomsequence generator is initialized according to the following equation atthe start of each OFDM symbol.c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)  Equation 7

Herein, N^(cell) _(ID) denotes a physical layer cell identifier.N_(CP)=1 for a normal CP and N_(CP)=0 for an extended CP.

In a 3GPP LTE system, a CRS is defined in a PRB pair. Referring to FIG.6, an RS sequence r_(l,ns)(m) for a CRS is mapped to complex modulationsymbols α^((p)) _(k,l) used as reference symbols for an antenna port pin a slot n_(s).α_(k,l) ^((p)) =r _(l,n)(m′)  Equation 8

Herein, k, l, and m′ are defined as follows.

$\begin{matrix}{\;{k = {{6\; m} + {\left( {v + v_{shift}} \right){mod}\; 6}}}} & {{Equation}\mspace{14mu} 9} \\{l = \left\{ \begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix} \right.} & \; \\{{m = 0},1,\ldots\mspace{14mu},{{2 \cdot N_{RB}^{DL}} - 1}} & \; \\{m^{\prime} = {m + N_{RB}^{\max,{DL}} - N_{RB}^{DL}}} & \;\end{matrix}$

Parameters v and v_(shift) define locations for different RSs in thefrequency domain and v is given by the following equation.

$\begin{matrix}{v = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}\mspace{11mu}{mod}\mspace{14mu} 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix} \right.} & {{Equation}\mspace{14mu} 10}\end{matrix}$

A cell-specific frequency shift is given by v_(shift)=N^(cell) _(ID) mod6, wherein N^(cell) _(ID) is a physical layer cell identifier, i.e., aphysical cell identifier.

FIG. 6 illustrates the structure of a UL subframe used in a wirelesscommunication system.

Referring to FIG. 6, a UL subframe may be divided into a data region anda control region in the frequency domain. One or several PUCCHs may beallocated to the control region to deliver UCI. One or several PUSCHsmay be allocated to the data region of the UE subframe to carry userdata.

In the UL subframe, subcarriers distant from a direct current (DC)subcarrier are used as the control region. In other words, subcarrierslocated at both ends of a UL transmission BW are allocated to transmitUCI. A DC subcarrier is a component unused for signal transmission andis mapped to a carrier frequency f₀ in a frequency up-conversionprocess. A PUCCH for one UE is allocated to an RB pair belonging toresources operating on one carrier frequency and RBs belonging to the RBpair occupy different subcarriers in two slots. The PUCCH allocated inthis way is expressed by frequency hopping of the RB pair allocated tothe PUCCH over a slot boundary. If frequency hopping is not applied, theRB pair occupies the same subcarriers.

The PUCCH may be used to transmit the following control information.

Scheduling request (SR): SR is information used to request a UL-SCHresource and is transmitted using an on-off keying (OOK) scheme.

HARQ-ACK: HARQ-ACK is a response to a PDCCH and/or a response to a DLdata packet (e.g. a codeword) on a PDSCH. HARQ-ACK indicates whether thePDCCH or PDSCH has been successfully received. 1-bit HARQ-ACK istransmitted in response to a single DL codeword and 2-bit HARQ-ACK istransmitted in response to two DL codewords. A HARQ-ACK responseincludes a positive ACK (simply, ACK), negative ACK (NACK),discontinuous transmission (DTX), or NACK/DRX. HARQ-ACK is usedinterchangeably with HARQ ACK/NACK and ACK/NACK.

Channel state information (CSI): CSI is feedback information for a DLchannel. CSI may include channel quality information (CQI), a precodingmatrix indicator (PMI), a precoding type indicator, and/or a rankindicator (RI). In the CSI, MIMO-related feedback information includesthe RI and the PMI. The RI indicates the number of streams or the numberof layers that the UE can receive through the same time-frequencyresource. The PMI is a value reflecting a space characteristic of achannel, indicating an index of a preferred precoding matrix for DLsignal transmission based on a metric such as an SINR. The CQI is avalue of channel strength, indicating a received SINR that can beobtained by the UE generally when the eNB uses the PMI.

A general wireless communication system transmits/receives data throughone downlink (DL) band and through one uplink (UL) band corresponding tothe DL band (in the case of frequency division duplex (FDD) mode), ordivides a prescribed radio frame into a UL time unit and a DL time unitin the time domain and transmits/receives data through the UL/DL timeunit (in the case of time division duplex (TDD) mode). Recently, to usea wider frequency band in recent wireless communication systems,introduction of carrier aggregation (or BW aggregation) technology thatuses a wider UL/DL BW by aggregating a plurality of UL/DL frequencyblocks has been discussed. A carrier aggregation (CA) is different froman orthogonal frequency division multiplexing (OFDM) system in that DLor UL communication is performed using a plurality of carrierfrequencies, whereas the OFDM system carries a base frequency banddivided into a plurality of orthogonal subcarriers on a single carrierfrequency to perform DL or UL communication. Hereinbelow, each ofcarriers aggregated by carrier aggregation will be referred to as acomponent carrier (CC).

For example, three 20 MHz CCs in each of UL and DL are aggregated tosupport a BW of 60 MHz. The CCs may be contiguous or non-contiguous inthe frequency domain. Although a case that a BW of UL CC and a BW of DLCC are the same and are symmetrical is described, a BW of each componentcarrier may be defined independently. In addition, asymmetric carrieraggregation where the number of UL CCs is different from the number ofDL CCs may be configured. A DL/UL CC for a specific UE may be referredto as a serving UL/DL CC configured at the specific UE.

In the meantime, the 3GPP LTE-A system uses a concept of cell to manageradio resources. The cell is defined by combination of downlinkresources and uplink resources, that is, combination of DL CC and UL CC.The cell may be configured by downlink resources only, or may beconfigured by downlink resources and uplink resources. If carrieraggregation is supported, linkage between a carrier frequency of thedownlink resources (or DL CC) and a carrier frequency of the uplinkresources (or UL CC) may be indicated by system information. Forexample, combination of the DL resources and the UL resources may beindicated by linkage of system information block type 2 (SIB2). In thiscase, the carrier frequency means a center frequency of each cell or CC.A cell operating on a primary frequency may be referred to as a primarycell (Pcell) or PCC, and a cell operating on a secondary frequency maybe referred to as a secondary cell (Scell) or SCC. The carriercorresponding to the Pcell on downlink will be referred to as a downlinkprimary CC (DL PCC), and the carrier corresponding to the Pcell onuplink will be referred to as an uplink primary CC (UL PCC). A Scellmeans a cell that may be configured after completion of radio resourcecontrol (RRC) connection establishment and used to provide additionalradio resources. The Scell may form a set of serving cells for the UEtogether with the Pcell in accordance with capabilities of the UE. Thecarrier corresponding to the Scell on the downlink will be referred toas downlink secondary CC (DL SCC), and the carrier corresponding to theScell on the uplink will be referred to as uplink secondary CC (UL SCC).Although the UE is in RRC-CONNECTED state, if it is not configured bycarrier aggregation or does not support carrier aggregation, a singleserving cell configured by the Pcell only exists.

The eNB may activate all or some of the serving cells configured in theUE or deactivate some of the serving cells for communication with theUE. The eNB may change the activated/deactivated cell, and may changethe number of cells which is/are activated or deactivated. If the eNBallocates available cells to the UE cell-specifically orUE-specifically, at least one of the allocated cells is not deactivatedunless cell allocation to the UE is fully reconfigured or unless the UEperforms handover. Such a cell which is not deactivated unless CCallocation to the UE is full reconfigured will be referred to as Pcell,and a cell which may be activated/deactivated freely by the eNB will bereferred to as Scell. The Pcell and the Scell may be identified fromeach other on the basis of the control information. For example,specific control information may be set to be transmitted and receivedthrough a specific cell only. This specific cell may be referred to asthe Pcell, and the other cell(s) may be referred to as Scell(s).

A configured cell refers to a cell in which CA is performed for a UEbased on measurement report from another eNB or UE among cells of an eNBand is configured for each UE. The configured cell for the UE may be aserving cell in terms of the UE. The configured cell for the UE, i.e.the serving cell, pre-reserves resources for ACK/NACK transmission forPDSCH transmission. An activated cell refers to a cell configured to beactually used for PDSCH/PUSCH transmission among configured cells forthe UE and CSI reporting and SRS transmission for PDSCH/PUSCHtransmission are performed on the activated cell. A deactivated cellrefers to a cell configured not to be used for PDSCH/PUSCH transmissionby the command of an eNB or the operation of a timer and CSI reportingand SRS transmission are stopped on the deactivated cell.

For reference, a carrier indicator (CI) means a serving cell indexServCellIndex and CI=0 is applied to a Pcell. The serving cell index isa short identity used to identify the serving cell and, for example, anyone of integers from 0 to ‘maximum number of carrier frequencies whichcan be configured for the UE at a time minus 1’ may be allocated to oneserving cell as the serving cell index. That is, the serving cell indexmay be a logical index used to identify a specific serving cell amongcells allocated to the UE rather than a physical index used to identifya specific carrier frequency among all carrier frequencies.

As described above, the term “cell” used in carrier aggregation isdifferentiated from the term “cell” indicating a certain geographicalarea where a communication service is provided by one eNB or one antennagroup.

The cell mentioned in the present invention means a cell of carrieraggregation which is combination of UL CC and DL CC unless specificallynoted.

Meanwhile, if RRH technology, cross-carrier scheduling technology, etc.are introduced, the amount of PDCCH which should be transmitted by theeNB is gradually increased. However, since a size of a control regionwithin which the PDCCH may be transmitted is the same as before, PDCCHtransmission acts as a bottleneck of system throughput. Although channelquality may be improved by the introduction of the aforementionedmulti-node system, application of various communication schemes, etc.,the introduction of a new control channel is required to apply thelegacy communication scheme and the carrier aggregation technology to amulti-node environment. Due to the need, a configuration of a newcontrol channel in a data region (hereinafter, referred to as PDSCHregion) not the legacy control region (hereinafter, referred to as PDCCHregion) has been discussed. Hereinafter, the new control channel will bereferred to as an enhanced PDCCH (hereinafter, referred to as EPDCCH).

The EPDCCH may be configured within rear OFDM symbols starting from aconfigured OFDM symbol, instead of front OFDM symbols of a subframe. TheEPDCCH may be configured using continuous frequency resources, or may beconfigured using discontinuous frequency resources for frequencydiversity. By using the EPDCCH, control information per node may betransmitted to a UE, and a problem that a legacy PDCCH region may not besufficient may be solved. For reference, the PDCCH may be transmittedthrough the same antenna port(s) as that(those) configured fortransmission of a CRS, and a UE configured to decode the PDCCH maydemodulate or decode the PDCCH by using the CRS. Unlike the PDCCHtransmitted based on the CRS, the EPDCCH is transmitted based on thedemodulation RS (hereinafter, DMRS). Accordingly, the UEdecodes/demodulates the PDCCH based on the CRS and decodes/demodulatesthe EPDCCH based on the DMRS. The DMRS associated with EPDCCH istransmitted on the same antenna port p∈{107,108,109,110} as theassociated EPDCCH physical resource, is present for EPDCCH demodulationonly if the EPDCCH transmission is associated with the correspondingantenna port, and is transmitted only on the PRB(s) upon which thecorresponding EPDCCH is mapped. For example, the REs occupied by theUE-RS(s) of the antenna port 7 or 8 may be occupied by the DMRS(s) ofthe antenna port 107 or 108 on the PRB to which the EPDCCH is mapped,and the REs occupied by the UE-RS(s) of antenna port 9 or 10 may beoccupied by the DMRS(s) of the antenna port 109 or 110 on the PRB towhich the EPDCCH is mapped. In other words, a certain number of REs areused on each RB pair for transmission of the DMRS for demodulation ofthe EPDCCH regardless of the UE or cell if the type of EPDCCH and thenumber of layers are the same as in the case of the UE-RS fordemodulation of the PDSCH.

Recently, machine type communication (MTC) has come to the fore as asignificant communication standard issue. MTC refers to exchange ofinformation between a machine and an eNB without involving persons orwith minimal human intervention. For example, MTC may be used for datacommunication for measurement/sensing/reporting such as meter reading,water level measurement, use of a surveillance camera, inventoryreporting of a vending machine, etc. and may also be used for automaticapplication or firmware update processes for a plurality of UEs. In MTC,the amount of transmission data is small and UL/DL data transmission orreception (hereinafter, transmission/reception) occurs occasionally. Inconsideration of such properties of MTC, it would be better in terms ofefficiency to reduce production cost and battery consumption of UEs forMTC (hereinafter, MTC UEs) according to data transmission rate. Sincethe MTC UE has low mobility, the channel environment thereof remainssubstantially the same. If an MTC UE is used for metering, reading of ameter, surveillance, and the like, the MTC UE is very likely to belocated in a place such as a basement, a warehouse, and mountain regionswhich the coverage of a typical eNB does not reach. In consideration ofthe purposes of the MTC UE, it is better for a signal for the MTC UE tohave wider coverage than the signal for the conventional UE(hereinafter, a legacy UE).

When considering the usage of the MTC UE, there is a high probabilitythat the MTC UE requires a signal of wide coverage compared with thelegacy UE. Therefore, if the eNB transmits a PDCCH, a PDSCH, etc. to theMTC UE using the same scheme as a scheme of transmitting the PDCCH, thePDSCH, etc. to the legacy UE, the MTC UE has difficulty in receiving thePDCCH, the PDSCH, etc. Therefore, the present invention proposes thatthe eNB apply a coverage enhancement scheme such as subframe repetition(repetition of a subframe with a signal) or subframe bundling upontransmission of a signal to the MTC UE having a coverage issue so thatthe MTC UE can effectively receive a signal transmitted by the eNB. Forexample, the PDCCH and/or the PDSCH may be transmitted to the MTC UEhaving the coverage issue through multiple (e.g., about 100) subframes.

FIG. 7 illustrates an exemplary signal band for MTC.

As one method of reducing the cost of an MTC UE, the MTC UE may operatein, for example, a reduced DL and UL bandwidths of 1.4 MHz regardless ofthe system bandwidth when the cell operates. In this case, a sub-band(i.e., narrowband) in which the MTC UE operates may always be positionedat the center of a cell (e.g., 6 center PRBs) as shown in FIG. 7(a), ormultiple sub-bands for MTC may be provided in one subframe to multiplexMTC UEs in the subframe such that the UEs use different sub-bands or usethe same sub-band which is not a sub-band consisting of the 6 centerPRBs as shown in FIG. 7(b).

In this case, the MTC UE may not normally receive a legacy PDCCHtransmitted through the entire system bandwidth, and therefore it maynot be preferable to transmit a PDCCH for the MTC UE in an OFDM symbolregion in which the legacy PDCCH is transmitted, due to an issue ofmultiplexing with a PDCCH transmitted for another UE. As one method toaddress this issue, introduction of a control channel transmitted in asub-band in which MTC operates for the MTC UE is needed. As a DL controlchannel for such low-complexity MTC UE, a legacy EPDCCH may be used.Alternatively, an M-PDCCH, which is a variant of the legacy EPDCCH, maybe introduced for the MTC UE.

A data channel (e.g., a PDSCH or a PUSCH) and/or a control channel(e.g., an M-PDCCH, a PUCCH, or a PHICH) may be transmitted repeatedlythrough multiple subframes or may be transmitted using a TTI bundlingscheme, for coverage enhancement (CE) of a UE. Additionally, for CE, thecontrol/data channel may be transmitted using a scheme such ascross-subframe channel estimation or frequency (narrowband) hopping.Herein, cross-subframe channel estimation refers to a channel estimationmethod using not only an RS in a subframe in which a correspondingchannel is present but also an RS in neighboring subframe(s).

An MTC UE may require CE up to, for example, 15 dB. However, all MTC UEsare not always under an environment requiring CE, nor are requirementsfor quality of service (QoS) of all MTC UEs the same. For example,devices such as a sensor and a meter have limited mobility and a smallamount of data transmission and reception and have a high possibility ofbeing located in a shadow area, thereby requiring high CE. However,wearable devices such as a smartwatch etc. may have greater mobility anda relatively large amount of data transmission and reception and have ahigh possibility of being located in a non-shadow area. Therefore, allMTC UEs do not necessarily require CE of a high level and demandedcapabilities of CE may differ according to types of MTC UEs.

In embodiments of the present invention, which will be described below,“assumes” may mean that an entity transmitting a channel transmits thechannel to match a corresponding “assumption” or that an entityreceiving the channel receives or decodes the channel in the form ofmatching the “assumption” on the premise that the channel has beentransmitted to match the “assumption”.

An LTE cell operates in a bandwidth of a minimum of 6 RBs. To furtherlower the cost of the MTC UE, an environment in which the MTC operatesthrough a narrow bandwidth of about 200 kHz may be considered. Such anMTC UE, i.e., the MTC UE capable of operating only within the narrowbandwidth, may also operate backward-compatibly in a legacy cell havinga wider bandwidth than 200 kHz. A clean frequency band in which thelegacy cell is not present may be deployed only for this MTC UE.

In the present invention, a system operating through a small narrowbandof one PRB or so in a legacy cell having a bandwidth wider than 200 kHzis referred to as in-band narrowband (NB) Internet of things (IoT) and asystem operating through a small NB of one PRB or so only for the MTC UEin a clean frequency band in which the legacy cell is not present isreferred to as stand-alone NB IoT.

IoT refers to internetworking of physical devices, connected devices,smart devices, buildings, and other items embedded with electronics,software, sensors, actuators, and network connectivity, which enablesthese objects to collect and exchange data. In other words, IoT refersto the network of physical objects, machines, people, and other devices,for enabling connectivity and communication to exchange data for IoTintelligent applications and services. IoT allows objects to be sensedand controlled remotely across existing network infrastructure, therebycreating opportunities for more direct integration of the physical worldinto the digital world and resulting in improved efficiency, accuracy,and economic benefits. Particularly, IoT using 3GPP technology is calledcellular IoT (CIoT).

NB-IoT allows access to network services through E-UTRA with a limitedchannel bandwidth of 180 kHz. NB-IoT may be considered to be IoToperating in units of one PRB.

Hereinafter, a radio resource of a size of one RB operating as NB-IoTwill be referred to as an NB-IoT cell or an NB-LTE cell and a systemsupporting an NB-IoT cell operating in one RB will be referred to as anNB-IoT system or an NB-LTE system.

In addition, hereinafter, an LTE radio resource on which communicationoccurs according to an LTE system will be referred to as an LTE cell anda GSM radio resource on which communication occurs according to a GSMsystem will be referred to as a GSM cell. An in-band NB IoT cell mayoperate in a bandwidth of 200 kHz (considering a guard band) or abandwidth of 180 kHz (without considering the guard band), in a systemband of an LTE cell.

The present invention proposes a method of providing, by an eNB, aservice to an NB device having NB RF capabilities while serving a UEhaving broadband RF capabilities in a broadband system. Herein,broadband represents a band of a minimum of 1.4 MHz.

The present invention proposes a method of receiving, by an NB devicehaving NB RF capabilities, a service using limited RF capabilities ofthe NB device while minimizing an effect on broadband UEs in a broadbandLTE system. Hereinafter, a UE supporting NB-IoT according to the presentinvention will be referred to as an NB-IoT UE or an NB-LTE UE.

A method of separately managing a frequency for initial access and afrequency for data and control channel transmission/reception other thaninitial access is proposed.

Hereinbelow, proposals of the present invention will be describedfocusing upon an NB-LTE UE. It should be noted that the proposals of thepresent invention described below are applicable to UEs operating in anormal small bandwidth (BW) as well as an NB-IoT UE.

In a legacy LTE/LTE-A system, a signal and system information forinitial access such as a PSS/SSS/PBCH are transmitted in 6 RBs (e.g.,1.4 MHz), which are positioned in the center of a channel band,regardless of an actual data transmission band of an eNB. Afterreceiving the PSS/SSS/PBCH, a UE may be aware of information such as aUL/DL timing of a corresponding cell, BW, application of FDD or TDD, asystem frame number (SFN), CP size (extended CP or normal CP), and aPCFICH. After successfully decoding the received PSS/SSS/PBCH andsuccessfully completing a random access procedure, the UE may determinethat the UE has successfully accessed a corresponding cell and thentransmit/receive UL/DL data on a desired corresponding cell. Since anNB-LTE UE having NB RF capabilities of 200 kHz is incapable of receiving6 RBs, the NB-LTE UE cannot even perform initial access in a legacyLTE/LTE-A system. Accordingly, an additional SS and system informationneed to be transmitted in a band having a BW of one RB corresponding toRF capabilities of the NB-LTE UE. To minimize an effect on the legacysystem and provide convenience of operation, the present inventionproposes operating a carrier on which an SS and system information forinitial access are transmitted (hereinafter, an anchor carrier) and acarrier for an actual data service (hereinafter, a data carrier). TheNB-LTE UE may perform initial access through the anchor carrier andreceive a data service on the data carrier indicated by the anchorcarrier.

Hereinafter, a method of operating an NB-IoT system (also called NB-LTEsystem) using an NB anchor carrier and an NB data carrier together withan LTE system in an LTE band will be described in more detail.Particularly, an operation scheme of an NB anchor/data carrier on whichthe NB-IoT system and the LTE system coexist in the LTE band, signalinginformation that should be transmitted to the LTE-NB UE on acorresponding carrier, and a UE operation will be described in moredetail. The NB-LTE system operates in a legacy broadband LTE system bandand needs to be designed to coexist with the LTE system in the same bandwhile minimizing an effect on a legacy eNB and a legacy UE.

Upon attempting to perform initial access to the LTE system, the UEfirst receives an SS that an eNB periodically transmits. In the LTEsystem, the eNB transmits a PSS/SSS through 6 center RBs (i.e., 1.08MHz) of a system band. Although the PSS/SSS is transmitted through the 6RBs, the center frequency of the 6 RBs in which the PSS/SSS is presentshould be located in a frequency corresponding to a multiple of 100 kHz.The UE performing a cell search searches for an SS of the PSS/SSS of theeNB in center frequencies corresponding to a multiple of 100 kHz inunits of 100 kHz. That is, in order to facilitate initial cell search ofthe UE, the DL center frequency of the LTE system may be located only inmultiples of 100 kHz in all available frequency bands. This is referredto as frequency raster or channel raster. If the channel raster of theUE is 100 kHz, the UE attempts to detect an SS in every 100 kHz in agiven frequency band. For example, if the channel raster is defined as100 kHz, the center frequency may be located only in the followingfrequency.F _(c) =F _(o) +m·100 kHz  Equation 11

Herein, m is an integer and F_(c) is a center frequency. F_(o) may be afrequency in which a frequency band in which an operation of the LTEsystem is allowed is started or a reference frequency which is used bythe UE when the UE starts to search for the center frequency in thefrequency band in which the operation of the LTE system is allowed.Alternatively, F_(o) may be a middle frequency of the LTE system, i.e.,a middle frequency of an EUTRA system. If the channel raster is definedas 100 kHz, the center frequency may be located only in units of 100kHz. According to Equation 11, the UE performs SS search only in unitsof every 100 kHz starting from the specific frequency F_(o) and assumesthat a frequency in which an SS of a system can be transmitted ispresent only in units of 100 kHz starting from F_(o).

The channel raster of the legacy LTE system is 100 kHz. Accordingly, itmay be considered that the channel raster of 100 kHz is maintained evenin the NB-LTE system. To minimize an effect on the legacy LTE system,maintaining a subcarrier spacing of 15 kHz used in the legacy LTE systemmay be considered in the NB-IoT system. Such considerations may beparticularly effective when the NB-IoT system operates within a band ofthe LTE system, i.e., an in-band. In this case, if the NB-IoT systemoperates in a guard band of the LTE system or a band distant fromband(s) used in the LTE system, subcarrier spacings other than 15 kHzmay be used to provide a service to more UEs in an NB.

Hereinbelow, a channel having a similar or identical purpose to achannel transmitted in a legacy broadband LTE system will be describedby adding “n” in front of the name of a legacy channel in order todistinguish the channel from a channel transmitted in the legacy LTEsystem. For example, an SS transmitted for the NB-LTE system will bereferred to as an nSS. The nSS may be transmitted by dividing the nSSinto an nPSS and an nSSS in a similar way to the LTE system or may betransmitted as one nSS without distinguishing between the nPSS and thenSSS. Similarly, in the case of a PBCH which is indispensable forinitial cell search, a PBCH transmitted in the NB-LTE system will bereferred to as an nPBCH. The transmission purpose and contents of abasic nPSS/nSSS/nPBCH are similar to those in the LTE system.

A transmission band of the nSS in the NB-LTE system is limited by RFcapabilities of the NB-LTE UE. That is, the transmission band of the nSScannot be transmitted in a band wider than a band determined by the RFcapabilities of the NB-LTE UE. The nSS should be transmitted in a bandequal to or narrower than a band determined by the RF capabilities ofthe NB-LTE UE so that the NB-LTE UE may necessarily receive the nSS. Forconvenience of description, proposals of the present invention aredescribed by taking an example in which the RF capabilities of theNB-LTE UE support 200 kHz. However, the described proposals of thepresent invention are not limited to the NB-LTE system having a BW of200 kHz.

Since the RF capabilities of the NB-LTE UE support 200 kHz, the nSS alsoneeds to be transmitted within 200 kHz. When taking into account thechannel raster of 100 kHz, it is preferred that the center frequency ofa band in which the nSS is transmitted is always a multiple of 100 kHz.In consideration of a guard band during transmission of a DL signal, ameaningful duration in which information is transmitted in the NB-LTEsystem may be 180 kHz. 180 kHz is a frequency band included in one PRBdefined in the current LTE system and includes 12 subcarriers when asubcarrier spacing of 15 kHz is considered. Locations at which the nSScan be transmitted are very restricted on the premise that the NB-LTEsystem coexists with the LTE system and the channel raster of the UE ismaintained at 100 kHz.

The following table shows a channel BW supported by the LTE system andthe number of RBs, N_(RB), per channel BW. That is, the following tableshows a transmission BW configuration N_(RB) in E-UTRA channel BWs.

TABLE 7 Channel bandwidth BW_(channel) [MHz] 1.4 3 5 10 15 20Transmission bandwidth 6 15 25 50 75 100 configuration N_(RB)

The LTE system supports 1.4, 3, 5, 10, 15, and 20 MHz as shown in Table7 and each band may be defined as the number of PRBs of a bandwidth of180 kHz.

The following table shows the size of a band, per channel BW of the LTEsystem, in which information is actually carried, and the size of aguard band in which information is not actually carried in acorresponding channel BW.

TABLE 8 Channel bandwidth Number of RBs Guard band Guard band/2 1.4 MHz6 RBs = 320 kHz 160 kHz 1080 kHz 3 MHz 15 RBs = 300 kHz 150 kHz 2700 kHz5 MHz 25 RBs = 500 kHz 250 kHz 4500 kHz 10 MHz 50 RBs = 1000 kHz 400 kHz9000 kHz 15 MHz 75 RBs = 1500 kHz 750 kHz 13500 kHz 20 MHz 100 RBs =2000 kHz 1000 kHz 18000 kHz

FIGS. 8 to 11 illustrate anchor carrier candidates according to an LTEchannel BW. Particularly, FIG. 8 illustrates the location of an anchorcarrier candidate on which an nSS may be present in an LTE band of 5MHz, FIG. 9 illustrates the location of an anchor carrier candidate onwhich an nSS may be present in an LTE band of 10 MHz, FIG. 10illustrates the location of an anchor carrier candidate on which an nSSmay be present in an LTE band of 15 MHz, and FIG. 11 illustrates thelocation of an anchor carrier candidate on which an nSS may be presentin an LTE band of 20 MHz. Referring to FIGS. 8 to 11, the nSS may betransmitted only at frequency location(s) represented as nSS carriercandidates.

A band consisting of odd-numbered RBs such as 5 MHz or 15 MHz includes acenter frequency of an anchor carrier at a location of a multiple of 900kHz from a center frequency thereof.

Referring to FIG. 8, a band of 180 MHz satisfying a channel raster of100 kHz and a subcarrier spacing of 15 kHz in a band of 5 MHz islimited, as illustrated in FIG. 8, to a total of 3 locations includingone center RB of 5 MHz and two RBs, each of which is included in a guardband located at each of both edges of a band of 5 MHz. Similarly,referring to FIG. 10, in a band of 15 MHz, a total of 11 PRBs maycorrespond to anchor carrier candidates.

In an LTE band of a specific size, in particular, in a system having anLTE channel BW consisting of even-numbered RBs, it is difficult todiscover a PRB, which matches PRB mapping of a legacy system within anin-band and is capable of transmitting an nSS satisfying a channelraster of 100 kHz while maintaining a subcarrier spacing of 15 kHz. Forexample, referring to FIG. 9, in a band of 10 MHz, a total of two PRBsmay correspond to anchor carrier candidates. Referring to FIG. 11, in aband of 20 MHz, a total of 6 PRBs may correspond to anchor carriercandidates. If there are few anchor subcarrier candidates as describedabove, it may be considered that an nSS of NB-LTE is transmitted over 2PRBs of a legacy carrier. However, such a configuration has ashortcoming of using more RBs than necessary. If the nSS is transmittedin-band, since an eNB should also support another legacy UE at the sametime, a degree to which the eNB can apply power boosting to the nSS maybe restricted and a limited power should be assumed to transmit the nSS.Such a situation may result in latency and degradation of cell detectioncapability when an NB-LTE UE performs initial cell acquisition. Toimprove the above situation, the present invention proposes transmittingthe nSS in a guard band even when NB-IoT is served in-band. For example,an anchor carrier on which the nSS is transmitted and a data carrierused to transmit/receive data after initial access may be separatelyoperated. In this case, in some embodiment(s) of the present invention,“data” in “data carrier” may collectively indicate control informationand system information after synchronization as well as a data channelsuch as a PDSCH/PUSCH.

FIG. 12 illustrates the status and transition of a UE according to thepresent invention.

An anchor carrier transmits basic system information for NB-LTE UE'sperforming initial access on an anchor carrier (S901) and informationabout a carrier on which channels other than an nSS/nPBCH aretransmitted, i.e., information about a data carrier. According to anembodiment of the present invention, the anchor carrier may be used totransmit the nSS/nPBCH but the data carrier is not used to transmit thenSS/nPBCH.

Referring to FIG. 11, the NB-LTE UE may monitor an RF thereof accordingto the anchor carrier (S901) and, when necessary, monitor the RFaccording to the data carrier (S903).

Over the nPBCH dedicated to transmission of system information, systeminformation of the anchor carrier and system information of the datacarrier may be transmitted. For example, the system information of theanchor carrier may include the number of antenna ports, a cell ID,and/or a system frame number (SFN) on the anchor carrier. The systeminformation of the data carrier will be described later. Informationabout the data carrier transmitted on the anchor carrier may betransmitted over the nPBCH. Alternatively, instead of transferring theinformation about the data carrier over the nPBCH, an additional channelmay be set to carry the information about the data carrier.

The NB-LTE UE receives an nSS on an initial anchor carrier to adjustsynchronization with the eNB, acquires system information about theinitial anchor carrier using the nPBCH, receives the information aboutthe data carrier, and then goes to the data carrier (T902) totransmit/receive data and a control channel. The anchor carrierbasically provides information about the location of the data carrier asthe information about the data carrier.

A relationship between the anchor carrier and the data carrier mayinclude the following cases (but does not exclude the other cases).

Anchor carrier within guard band+same power amplifier (PA)—data carrierwithin in-band: When the same PA is used for the anchor carrier and thedata carrier, it may be assumed that the cell ID, the SFN, etc. areshared between the anchor carrier and the data carrier and it may beassumed that time/frequency tracking values are equal. That is, when thesame PA is used for the anchor carrier and the data carrier, the samecell ID and the same SFN are used for the anchor carrier and the datacarrier. If frequency spacing between the in-band and the guard band arenot wide, it may be assumed that the time/frequency tracking values areequal. The data carrier in the in-band may have a cell ID and/or an SFNof LTE.

Anchor carrier within guard band+different PA—data carrier withinin-band: If different PAs are used for the anchor carrier and the datacarrier, cell IDs, SFNs, etc. in the anchor carrier and the data carriermay be different. If different PAs are used for the anchor carrier andthe data carrier, a cell ID and an SFN of the data carrier may betransmitted on the anchor carrier. The data carrier in the in-band mayhave a cell ID and/or an SFN of LTE and the anchor carrier in the guardband may have a cell ID and/or an SFN different from the cell ID and/orthe SFN of LTE. If frequency spacing between the in-band and the guardband are wide, it may be assumed that the time/frequency tracking valuesare equal. If the frequency spacing between the in-band and the guardband are not wide, it may be desirable that tracking values of the datacarrier and the anchor carrier be different. In this case, sincetime/frequency tracking for the data carrier needs to be newlyperformed, an offset value for a frame/subframe index in which an nSS ofthe data carrier is transmitted may be transmitted through the anchorcarrier. Information about a difference in transmission power betweenthe anchor carrier and the data carrier or a value of transmission powerof the data carrier may also be transmitted through the anchor carrier.

Anchor carrier within guard band+data carrier within guard band: In thiscase, the same PA or different PAs may be assumed. To distinguishbetween the case in which the same PA is used and the case in whichdifferent PAs are used, information as to whether the NB-LTE UE mayassume the same PA (or the same cell ID, the same SFN, etc.) may beadditionally transmitted.

Anchor carrier within in-band+data carrier within guard band: If it isdesired to use a guard band and an in-band which are adjacent, the eNBmay configure the anchor carrier in the in-band and inform NB-LTE UEs ofa frequency offset of a carrier of the guard band.

Anchor carrier within in-band+data carrier within in-band: In this case,the same PA or different PAs may be assumed. To distinguish between thecase in which the same PA is used and the case in which different PAsare used, information as to whether the NB-LTE UE may assume the same PA(or the same cell ID, the same SFN, etc.) may be additionallytransmitted.

In particular, if the anchor carrier is operated in the guard band, anNB-LTE system may be operated in the in-band and the guard band,regardless of an LTE system bandwidth. In the guard band or a band otherthan an LTE system band, since there is no restriction on physicalsignals (e.g., a PDCCH region, a PSS/SSS, a PBCH resource, etc.) of theLTE system, collision between an NB-IoT signal and the physical signalsof the LTE system may not be considered. For example, if the anchorcarrier is configured in the guard band and the data carrier isconfigured to operate in a PRB except for 6 center PRBs in which thePSS/SSS and the PBCH are occupied, the eNB may provide a data service tothe NB-LTE UE on the data carrier without considering collision betweenthe PSS/SSS/PBCH and the nSS and the NB-LTE UE may transmit/receive datathereof on the data carrier without considering the presence of thePSS/SSS/PBCH.

The NB-LTE UE may acquire information about the data carrier afterforming association by accessing one anchor carrier or acquire theinformation about the data carrier through system information of theanchor carrier. For example, the information about the data carrier maybe represented as a list of frequencies of the data carrier. Thelocation of the data carrier may be represented as a gap between acenter frequency of the anchor carrier and a center frequency of thedata carrier. There may be one or more data carriers. In this case,information necessary for communication on a corresponding data carrierfor each data carrier may be transmitted. For example, information aboutdata carrier(s) may be transmitted in the form ofData_carrier={nData_carrier_1, nData_carrier_2, nData_carrier_3, . . . }and information necessary to receive data and other channels for eachdata carrier may be transmitted. The eNB may configure a plurality of DLcarriers and a plurality of UL carriers. One data carrier may consist ofone UL carrier and one DL carrier. For example, the eNB may transmitdata carrier information including information indicating a data DLcarrier (nData_downlink_carrier) for NB-IoT and information indicating adata UL carrier (nData_uplink_carrier) for NB-IoT (e.g.,Data_Data_carrier_1={nData_downlink_carrier_1, nData_uplink_carrier_1}).If a plurality of data carriers is configured, a UL carrier and a DLcarrier may be separately configured. For example, information ofData_Carrier={nData_downlink_carrier_1, nData_downlink_carrier_2,nData_downlink_carrier_3, nData_uplink_carrier_1,nData_uplink_carrier_2}) may be transmitted by the eNB.

Accordingly, synchronization and basic information may be transmittedthrough a frequency matching channel raster and a list of frequenciesfor an additional NB-LTE carrier may be provided. Therefore, an NB-LTEcarrier having a center frequency in a frequency which does not match achannel raster of 100 kHz may be configured.

Upon configuring a UL carrier, the eNB may indicate an additional ULcarrier for transmission of a random access channel for NB-IoT(hereinafter, nRACH). If no signaling is given, the NB-LTE UE maytransmit all configured UL carrier nRACHs.

Hereinafter, a method of receiving DL channel(s) by the NB-IoT UE on theanchor carrier will be described.

When a plurality of data carriers are configured, since the NB-LTE UE isgenerally implemented with low-cost/low-complexity, the plural datacarriers are not simultaneously monitored and only one data carrier at atime may be sequentially monitored. In this case, the NB-LTE UE may moveto each data carrier at an interval indicated by the eNB or apredetermined time interval to receive a channel such as data etc.Information about an interval at which the NB-LTE UE can monitor thedata carrier may be provided when information about the data carrier isprovided through the anchor carrier. As another method, the eNB maytransmit a transition command from a corresponding data carrier, inwhich a channel such as an nPDSCH/nPDCCH is transmitted, to another datacarrier. For example, if the NB-LTE UE is receiving the nPDCCH/nPDSCH innData_Carrier_1, the eNB may command the NB-LTE UE to move tonData_carrier_2 in the nPDSCH at a specific timing. This process may beimplicitly performed through frequency hopping between multiple datacarriers. In this case, the eNB may transmit a list of carriers (i.e., alist of PRBs) on which frequency hopping is to be performed.

The NB-LTE UE first searches for the anchor carrier to receive the nSSand succeeds in performing initial access by successfully receiving thenSS/nPBCH. Upon succeeding in receiving the nSS on a carrier, the NB-LTEUE may acquire a cell ID used for signal transmission/reception on thecarrier from the nSS. Upon successfully performing initial access, theNB-LTE UE may perform an operation of receiving a channel such as dataafter moving to the data carrier indicated by the anchor carrier.Information about the data carrier transmitted on the anchor carrier mayinclude the location of the data carrier, for example, a gap between acenter frequency of the anchor carrier and a center frequency of thedata carrier, PDSCH rate-matching information of the data carrier, CRSinformation on the data carrier, a CP type (e.g., a normal CP or anextended CP), a frame structure type (e.g., TDD or FDD), a PDSCH startsymbol number, information about an SFN, TDD UL/DL configuration (referto Table 1) in the case of TDD, and/or a subcarrier spacing. The PDSCHrate-matching information on the data carrier may include informationabout a CRS location as the most representative example. For example, “aPDSCH is rate-matched at a CRS location” may indicate that a PDSCHsignal is not mapped to REs on which the CRS is present. Hereinafter, “aCRS is rate-matched” indicates that the eNB does not map other DLsignals (e.g., an nPDCCH and/or nPDSCH) to frequency-time resource(s) onwhich the CRS is mapped and indicates that the UE receives or decodescorresponding data under that assumption that other DL signals are notmapped to the frequency-time resource(s) on which the CRS is mapped.That is, unlike a puncturing operation for mapping a signal andtransmitting the signal at parts except for a part of being mapped to acorresponding frequency-time resource, no data signal is mapped to arate-matched frequency-time resource. Accordingly, a frequency-timeresource punctured in a resource mapping process of a signal is countedas a resource of the signal but a signal part mapped to a puncturedfrequency-time resource is not actually transmitted. On the other hand,a rate-matched frequency-time resource is not counted as a resource ofthe signal. Accordingly, since a PDSCH signal is rate-matched on REs onwhich the CRS is present, the eNB does not use RE(s) used for CRStransmission to transmit the nPDCCH/nPDSCH and the UE may assume thatthe RE(s) assumed to be used for CRS transmission are not used totransmit the nPDCCH/nPDSCH. Information about the number of CRS antennaports and a CRS frequency location (i.e., frequency shift v_(shift)) onthe data carrier should be transmitted. The information corresponding tothe frequency shift v_(shift) may be a frequency shift v_(shift)represented as one value among 0, 1, and 2 or cell ID information usedto generate a CRS sequence. In addition, transmission mode (TM)information used in a broadband LTE system on the data carrier andinformation such as a CSI-RS may be signaled as the information aboutthe data carrier. Information about a CSI-RS location that the NB-LTE UEshould rate-match on the data carrier may also be provided.

For convenience of an operation of the NB-IoT system, a CP type, a framestructure, TDD UL/DL configuration, and subcarrier spacing information,on the data carrier, may be configured to be the same as those on theanchor carrier. In this case, the NB-LTE UE may assume that the CP type,the frame structure, the TDD UL/DL configuration, and the subcarrierspacing information, on the data carrier, are the same as those on theanchor carrier. If the CP type, the frame structure, the TDD UL/DLconfiguration, and the subcarrier spacing information, on the datacarrier, are defined to be the same as those on the anchor carrier, suchinformation may not be additionally signaled.

It may be assumed that an SFN in the LTE system is aligned with an SFNin the NB-LTE system. That is, it may be assumed that the SFN on thedata carrier is equal to the SFN on the anchor carrier. If the SFN onthe data carrier is not equal to the SFN on the anchor carrier, adifference between the SFN of the anchor carrier and the SFN of the datacarrier may be signaled.

FIG. 13 illustrates a relationship between a (legacy) CRS and an in-bandIoT carrier according to the present invention.

The following descriptions may be considered in the above-describedembodiments of the present invention.

A multi-PRB operation permits a UE to change from an anchor carrier toan additional carrier, i.e., a non-anchor carrier, or from thenon-anchor carrier to the anchor carrier. For example, the UE operatingin multiple PRBs may change a carrier that the UE monitors from ananchor carrier within an in-band to an additional carrier within a guardband, from an anchor carrier within the guard band to an additionalcarrier within the in-band, from the anchor carrier within the guardband to an additional carrier within the guard band, or from the anchorcarrier within the in-band to the additional carrier within the in-band.If the UE changes a carrier from the in-band to the guard band, it maybe only necessary to indicate that an additional PRB is present withinthe guard band. If the UE changes a carrier to another carrier withinthe in-band, it is necessary to clarify how to indicate in-band specificparameters among the following parameters. The eNB needs to inform theUE of information about a cell ID of a PRB within the in-band andinformation about a CRS. For simplicity, information about whether acell ID of an in-band PRB is equal to that of a PRB within the guardband or the in-band may be provided. For example, when the UEtransitions from an anchor PRB to an in-band PRB, if a cell ID of thein-band PRB is equal to a cell ID of the anchor PRB, the UE may derivethe frequency shift v_(shift) based on frequency information (e.g., aPRB index, an offset from a center frequency, etc.) and the cell ID.Conversely, if they are not equal, the cell ID of the in-band PRB andlocations of CRS ports needed by the UE to perform data rate matchingmay be provided from the anchor PRB (i.e., anchor carrier). As can beappreciated from FIG. 5, Equation 9, and Equation 10, since thelocations of CRS ports, i.e., locations of REs on which the CRS ismapped, become different according to the number of CRS ports and thecell ID, information about the number of CRS ports and the cell IDapplied to the CRS may be provided as rate-matching information. Inaddition, in order to receive a PDSCH within the in-band, the UErequires information about a start location of DL data (e.g., a PDSCH)in a corresponding PRB within the in-band and information about thenumber of OFDM symbols for a DL control channel. For example, thefollowing information may be provided.

Same physical cell identity (PCI) (or information as to whether a cellID of a PRB in the in-band is equal to that of an anchor PRB) (S1310)

When a same PCI field indicates True (S1310, TRUE),

If this field indicates True, it is assumed that a cell ID obtained fromthe anchor carrier is the same as a host cell ID within an additionalPRB in the in-band, which is similar to the case of the in-band. In thiscase, the host cell ID may mean an LTE cell having a PRB in which anNB-IoT cell operates, i.e., an EUTRA cell.

If this field indicates True, it may be assumed that the same number ofantenna port(s) as the number of antenna port(s) used for an RS forNB-IoT (hereinafter, an NB-RS or an NRS) within an anchor PRB(hereinafter, NRS ports) is used to transmit a legacy CRS (S1330). Forexample, when there are two NRS ports, the UE may receive data in acorresponding PRB under the assumption that CRSs are present atlocations obtained by applying v_(shift) to locations of REs representedas CRS port 0 and CRS port 1 in FIG. 5.

Further, if this field indicates True, the UE may assume thatinformation of the NRS within the anchor PRB is the same as informationof a CRS of a host cell. The meaning of “information of the NRS is thesame as information of a CRS of a host cell” may indicate that thenumber of antenna ports of the NRS is the same as the number of antennaports of the CRS and an RE location at which the NRS is transmitted isthe same as an RE location at which the CRS is transmitted. In addition,the UE may receive a control signal and data under the assumption thatthe CRS is an NRS in a corresponding in-band. In this case, uponreceiving data in a corresponding PRB, the UE may rate-match a CRS RElocation and use the CRS to receive/demodulate the control signal andthe data.

If frequency information is given by an offset from the center, CRS PRBinformation may be implicitly derived from additional PRB frequencyinformation.

When the same PCI field does not indicate True (S1310, FALSE),

If this field does not indicate True, it is necessary to clarify whetherthe UE can still assume the same v_(shift) value based on a cell IDsearched for from the anchor PRB. To reduce signaling overhead, the samev_(shift) value is assumed and only the number of CRS antenna ports(hereinafter, CRS ports) may be indicated (S1350). The UE may assumethat CRS ports corresponding to the number of indicated CRS ports areused for CRS transmission in a corresponding PRB and receive data(S1350). For example, if the number of indicated CRS ports is 4, the UEmay assume that CRSs are present at locations obtained by applyingv_(shift) to RE locations represented as CRS ports 0 to 3 in FIG. 5 andreceive data in the PRB. If the number of CRS antenna ports is notsignaled, the UE may assume that a maximum number of CRS ports (e.g., 4ports) is used to rate-match data.

Control format indicator (CFI) (or a start location of a PDSCH or annPDCCH is indicated).

To cause the UE to receive a control channel (e.g., nPDCCH) and a datachannel (e.g., nPDSCH) within a data PRB of the UE, information about asymbol duration in which the nPDCCH is transmitted and information abouta symbol location at which nPDSCH transmission is started may besignaled to the UE.

Alternatively, instead of signaling LTE CRS information within the dataPRB in association with a cell ID as described above, a legacy CRS maynot be used any more in an additional PRB and the number of CRS antennaports may be configured for the UE only to perform data rate matching.That is, the UE may decode or demodulate the nPDSCH/nPDCCH based on onlythe NRS without using the CRS, wherein the UE may receive, decode, ordemodulate the nPDSCH/nPDCCH under the assumption that the nPDSCH/nPDCCHis not mapped to RE(s) on which the CRS is present. In this case, the UEmay assume that v_(shift) of the NRS which has been acquired from ananchor carrier and has already been known to the UE is equal tov_(shift) of the CRS in the additional PRB. That is, the UE decodes ordemodulates the nPDSCH/nPDCCH based on only the NRS without using theCRS, wherein the UE may receive, decode, or demodulate the nPDSCH/nPDCCHunder the assumption that the nPDSCH/nPDCCH is not mapped on RE(s) onwhich the CRS is present.

As proposed above, offloading from the anchor carrier to the datacarrier may be performed using one of the following methods.

Method 1. This method provides a list of potential data carrier(s)through additional system information and permits the UE to search foranother carrier (in the list).

Method 2. Explicit offloading. This method explicitly configures hoppingto the data carrier after cell association.

Method 3. In this method, the anchor carrier provides only systeminformation necessary to locate an nSS and data carrier(s). In thiscase, the UE cannot form cell association with the anchor carrier andthe anchor carrier may be assumed to be a carrier simply giving onlyinformation about the data carrier.

If the anchor carrier is used only for synchronization according toMethod 3, SSs may be successively transmitted to cause the UE to rapidlydetect the SSs. That is, an SS transmission scheme of the data carriermay be different from an SS transmission scheme of the anchor carrier.In this case, if the UE does not succeed in performing blind detectionof an SS according to the SS transmission scheme of the anchor carrier,the UE may perform blind detection for an SS on the data carrieraccording to the SS transmission scheme of the data carrier.

Alternatively, if it is assumed that Method 3 is used, the UE may detectthe nSS under the assumption that a CRS or a legacy PDCCH region is notpresent in a subframe in which the nSS may generally be present. Asystem desired to support IoT in an in-band may mandate SS transmissionthrough a guard band. On the premise that the nSS is always transmittedin the guard band, a subcarrier spacing for SS transmission may differfrom a subcarrier spacing in the in-band. In other words, the subcarrierspacing in which the nSS is transmitted may differ from a subcarrierspacing of the in-band. On the premise that the nSS is alwaystransmitted in the guard band, a subcarrier spacing for SS transmissionmay differ from a subcarrier spacing in the in-band. In other words, asubcarrier spacing in which the nSS is transmitted may differ from asubcarrier spacing of the in-band.

In addition, if the nSS is transmitted in the guard band to support thein-band according to embodiment(s) of the present invention, the nSS maynot be present in the in-band and the nSS may be transmitted only on theanchor carrier. That is, the UE may assume that the nSS is present onlyon the anchor carrier and no nSS is present on the data carrier withinthe in-band. In this case, the UE may assume that the transmission powerof the nSS in the guard band is the same as the transmission power ofdata or a CRS in the in-band and that an SFN/time/frequency in the guardband is the same as that in the in-band.

If the nSS is transmitted only on the anchor carrier of the guard band,all OFDM symbols on the anchor carrier may be used to transmit the nSSand the nSS may be transmitted in multiple subframes.

In order for the NB-LTE UE to move to the data carrier and receive achannel such as data, the eNB should signal information about an RS forreception of a data channel and/or a control channel. Hereinafter, adata channel configured on the data carrier for NB-IoT will be referredto as an nPDSCH and a control channel configured on the data carrier forNB-IoT will be referred to as an nPDCCH. RSs used for the nPDSCH and thenPDCCH may broadly include a CRS and a DM-RS (i.e., UE-RS). When the CRSis used, the eNB may inform the UE of information about a cell ID usedfor the CRS on the data carrier. This cell ID may be the same as a cellID used for an nSS sequence on the anchor carrier. If the cell ID usedfor the CRS on the data carrier is the same as the cell ID used for thenSS on the anchor carrier, the NB-LTE UE may use the CRS to receive thenPDSCH or the nPDCCH using the cell ID of the nSS when additional cellID is not signaled. If a DM-RS is used, the eNB should inform the UE ofinformation about a DM-RS sequence.

Upon moving to the data carrier, the NB-LTE UE may receive a channelsuch as an nPDCCH/nPDSCH thereof on an OFDM symbol after an OFDM symbolon which a broad band PDCCH is transmitted in a corresponding band. If aPDSCH start symbol indicated by the anchor carrier is an OFDM symbol n,the NB-LTE UE may receive the channel such as the nPDCCH/nPDSCH for theNB-LTE-UE starting from the OFDM symbol n.

While monitoring the data carrier for a predetermined time, the NB-LTEUE receiving the channel such as the nPDCCH/nPDSCH on the data carrierreturns to the anchor carrier at a specific timing and monitors theanchor carrier. The NB-LTE UE may go to the anchor carrier according toa predetermined period (T904) and monitor the anchor carrier (S901). Ifthe nSS/nPBCH is periodically transmitted, the NB-LTE UE may move to theanchor carrier to receive a corresponding channel in every duration inwhich the channel is transmitted. In addition, if the eNB indicates thatthe NB-LTE UE receiving a channel such as data on the data carriershould go to the anchor carrier to receive a specific channel, theNB-LTE UE should go to the anchor carrier. Upon waking up from adiscontinuous reception (DRX) state, the NB-LTE UE may always go to theanchor carrier (T904), receive the nSS/nPBCH through the anchor carrier(S901), and then go to the data carrier (T902).

Hereinafter, in operating an NB-LTE system using two types of carriers,i.e., the anchor carrier and the data carrier, according to the presentinvention, system information and SS transmission schemes will bedescribed in more detail.

The present invention has been schematically described in considerationof the nSS and the nPBCH transmitted only on the anchor carrier. Anembodiment different from the embodiment in which the nSS and nPBCH arepresent only on the anchor carrier may be considered. Only an MIB may betransmitted on the anchor carrier and an nSS for partial system updatemay be transmitted through an additional channel of the data carrier.Moreover, an additional nSS may be transmitted on the data carrier. Inthis case, the nSS transmitted on the data carrier may be lessfrequently transmitted and may be an SS used only for the purpose ofsynchronization reacquisition. The nSS transmitted on the data carriermay be the same as the nSS transmitted on the anchor carrier. However,to raise the efficiency of resource usage, the nSS transmitted on thedata carrier may be designed differently from the nSS transmitted onanchor carrier. For example, the nSS transmitted on the anchor carriermay be transmitted separately as two signals of an nPSS and an nSSS andthe nSS transmitted on the data carrier may be transmitted only aseither the nPSS or the nSSS. Alternatively, an additional signal usedonly for reacquisition may be transmitted on the data carrier.

If the nSS and system information are transmitted even on the datacarrier, initial cell search is performed only on the anchor carrier andthe NB-LTE UE which has successfully performed initial access after cellsearch does not need to move to the anchor carrier any longer. That is,a carrier carrying a (relatively frequently transmitted) nSS and annPBCH for initial cell search is configured and an nSS for systeminformation update and reacquisition except for initial cell search, andother data may be transmitted on an additional carrier.

The anchor carrier and the data carrier may be differently operatedaccording to the type of a signal/channel transmitted/received on eachcarrier. Hereinbelow, the above-described basic scheme in which the nSSand the nPBCH are transmitted on the anchor carrier and signals/channelsother than the nSS/nPBCH are transmitted on the data carrier will bemodified and the modified scheme will be applied to a legacy LTE systemband. A frequency band usable in an NB-LTE system according to thepresent invention is categorized into three bands, i.e., an in-band usedby a legacy LTE system, a guard band of the LTE system, and a band(e.g., GSM band) which can be operated regardless of the LTE system inan additional frequency band other than a band used in the LTE system.As described above, it may be impossible, in an in-band of a specificLTE system band, to search for a band location of 180 kHz satisfying asubcarrier spacing of 15 kHz and a raster of 100 kHz for initial cellaccess. Obviously, an NB-IoT cell location in the in-band of the LTEsystem band may be easily searched according to an LTE system band. Toconsistently perform initial cell search regardless of the system band,the present invention has proposed operating the anchor carrier and thedata carrier. However, if there are many lists of data carriers, it maybe difficult to operate the anchor carrier and the data carrier. Forexample, if the data carrier(s) which can be used by the NB-LTE UE whichhas performed initial access in the anchor carrier are indicated by thenPBCH, the nPBCH needs to carry master system information (e.g., MIB) ofthe anchor carrier and (master) system information of the datacarrier(s). In this case, it may be difficult to transmit both thesystem information of the anchor carrier and the system information ofthe data carrier(s) through the nPBCH. In addition, a subcarrier spacingused on the anchor carrier may be different from a subcarrier spacingused on the data carrier. For convenience and consistency of systemdesign, the anchor carrier may operate as a stand-alone carrier in aguard band or in a band other than the LTE system band. Accordingly,only information about an nPSS/nSSS and master system information forperforming only initial access may be transmitted on the anchor carrierand only a frequency location of the data carrier may be indicated asinformation about the data carrier so that the amount of systeminformation provided through the anchor carrier can be minimized. TheNB-LTE UE which has received such information and succeeded inperforming initial access may move to a signaled data carrier andreceive data on the data carrier. When there are plural data carriers,only a specific number of data carriers (e.g., a specific number of DLcarriers and/or a specific number of UL carriers) among the plural datacarriers may be indicated by the anchor carrier. System informationabout a plurality of actual data carriers is provided throughcorresponding data carriers. For example, a plurality of data carriersmay be configured for the NB-LTE system. Thereamong, information such asan nSS for reacquisition and system information for the data carriersmay be transmitted on some data carriers and control/data channels maybe transmitted on the other data carriers. In other words, initial cellaccess may be performed on the anchor carrier and data carrier(s) may bedivided into an IoT carrier on which system information about the datacarriers and an nSS transmitted with low density are transmitted anddata carriers on which the data channel and the control channel aretransmitted. Since the IoT carrier is located in an in-band of the LTEsystem although the IoT carrier performs a partial synchronizationfunction, there may be a restriction on locations of available REs andavailable symbols for minimizing interference to the LTE system. Incontrast, since the anchor carrier may be located in a guard band andother bands, a degree of freedom is further raised for the usage offrequency and time resources. System information and rate-matchinginformation of the IoT carrier and the data carrier may be the same. TheIoT carrier and the data carrier become different according to whethersystem information through a corresponding carrier is transmitted andwhether an nSS is transmitted. When the anchor carrier indicates thedata carrier on which the UE should move for a data service afterinitial access, only information about the IoT carrier and basic systeminformation for the IoT carrier are transmitted and the NB-LTE UE whichhas moved to the IoT carrier may receive system information about thedata carrier and information such as a rate-matching pattern through aspecific channel on the IoT carrier. Upon waking up from DRX, the NB-LTEUE may not move to the anchor carrier, may perform reacquisition, andmay move to a specific data carrier after receiving system informationabout the data carrier.

FIG. 14 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

The transmitting device 10 and the receiving device 20 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedembodiments of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 10 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into K layers through demultiplexing, channel coding,scrambling, and modulation. The coded data stream is also referred to asa codeword and is equivalent to a transport block which is a data blockprovided by a MAC layer. One transport block (TB) is coded into onecodeword and each codeword is transmitted to the receiving device in theform of one or more layers. For frequency up-conversion, the RF unit 13may include an oscillator. The RF unit 13 may include N_(t) (where N_(t)is a positive integer) transmit antennas.

A signal processing process of the receiving device 20 is the reverse ofthe signal processing process of the transmitting device 10. Undercontrol of the processor 21, the RF unit 23 of the receiving device 20receives radio signals transmitted by the transmitting device 10. The RFunit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 10 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 20. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 20 and enables the receiving device 20 to derivechannel estimation for the antenna, irrespective of whether the channelrepresents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 20 in UL and as the transmitting device 10 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

The eNB processor of the present invention may control the eNB RF unitto transmit an nSS/nPBCH on an anchor carrier according to any one ofthe proposals of the present invention. The eNB processor may controlthe eNB RF unit to transmit information about data carrier(s)(hereinafter, data carrier information) which is to be used totransmit/receive a data/control channel for a specific UE on the anchorcarrier. The eNB processor may control the eNB RF unit to transmit a DLcontrol/data channel (e.g., an nPDCCH and/or an nPDSCH) to the UE on anyone of the data carrier(s). The eNB processor may control the eNB RFunit to receive a UL control/data channel (e.g., an nPUCCH and/or annPUSCH) from the UE on any one of the data carrier(s).

The UE processor of the present invention may control the UE RF unit toattempt to receive the nSS/nPBCH on anchor carriers each having achannel bandwidth of one RB or may attempt to decode the nSS/nPBCHaccording to any one of the proposals of the present invention. Uponsucceeding in receiving or decoding the nSS/nPBCH, the UE processor maycontrol the UE RF unit to receive data carrier information about a datacarrier which is to be used to transmit/receive a control/data channelof the UE on a corresponding anchor carrier. The UE processor maycontrol the UE RF unit to receive the DL control/data channel (e.g., thenPDCCH and/or the nPDSCH) on any one of data carrier(s) based on thedata carrier information. The UE processor may control the UE RF unit totransmit the UL control/data channel (e.g., the nPUCCH and/or thenPUSCH) on any one of data carrier(s) based on the data carrierinformation.

The eNB processor of the present invention may control the eNB RF unitto transmit information about a cell ID (hereinafter, a first cell ID)of an NB-IoT carrier according to any one of the proposals of thepresent invention. The eNB processor may control the eNB RF unit totransmit the DL signal (e.g., the nPDCCH and/or the nPDSCH) on theNB-IoT carrier. The NB-IoT carrier may be, for example, a carrieroperating in one PRB within a channel band of an LTE system. In thiscase, processing of a CRS transmitted in an LTE cell may be problematic.If the NB-IoT carrier operates in an in-band PRB, the eNB processor maycontrol the eNB RF unit to transmit cell ID information indicatingwhether a cell ID (hereinafter, a second cell ID) used for a (legacy)CRS on the NB-IoT carrier is the same as or different from the firstcell ID.

If the second cell ID is the same as the first cell ID, the eNBprocessor may control the eNB RF unit to transmit the CRS on the NB-IoTcarrier through the same number of antenna ports as the number ofantenna ports (hereinafter, the NRS ports) used for transmission of an.

If the second cell ID is different from the first cell ID, the eNBprocessor may control the eNB RF unit to transmit number-of-CRS portsinformation indicating the number of antenna ports (hereinafter, CRSports) used for transmission of the CRS. The number of CRS ports and thenumber of NRS ports may be equal or different. However, if the secondcell ID and the first cell ID are different, since this means that acell ID used for transmission of the CRS is different from a cell IDused for transmission of the NRS, a CRS resource location forrate-matching may be different according to a cell ID even when thenumber of CRS ports is the same as the number of NRS ports. Accordingly,if the second cell ID is different from the first cell ID, the eNBprocessor according to the present invention may control the eNB RF unitto transmit the information indicating the number of CRS ports to theUE. The eNB processor may control the eNB RF unit to transmit the CRS onthe NB-IoT carrier through CRS ports of a number corresponding to thenumber-of-CRS ports information.

Upon transmitting the CRS on the NB-IoT carrier, the eNB processor maycontrol the eNB RF unit to transmit the CRS at a frequency location(refer to Equation 9 and Equation 10) obtained by applying a frequencyshift v_(shift) based on the second cell ID. The eNB processor maygenerate the NRS based on the second cell ID and control the eNB RF unitto transmit the NRS on the NB-IoT carrier.

The eNB processor may control the eNB RF unit to transmit carrierinformation about the NB-IoT carrier (hereinafter, a data carrier) on adifferent NB-IoT carrier (hereinafter, an anchor carrier) from theNB-IoT carrier. The carrier information may include informationindicating a cell ID of the data carrier. For example, the cell ID maybe (implicitly) transmitted through an nSS transmitted on the anchorcarrier. In other words, the cell ID transmitted on the anchor carriermay be applied to the data carrier. The data carrier may be a carrierwithout the nSS/nPBCH and the anchor carrier may be a carrier with thenSS/nPBCH. The anchor carrier may be a carrier operating in a PRB withina guard band of the channel band used in the LTE system.

The UE processor of the present invention may control the UE RF unit toreceive the information about the cell ID (hereinafter, the first cellID) of the NB-IoT carrier according to any one of the proposals of thepresent invention. The UE processor may control the UE RF unit toreceive the DL signal (e.g., the nPDCCH and/or the nPDSCH) on the NB-IoTcarrier. The NB-IoT carrier may be, for example, a carrier operating inone PRB within the channel band of the LTE system. In this case,processing of the CRS transmitted in the LTE cell may be problematic. Ifthe NB-IoT carrier operates in an in-band PRB, the UE RF unit mayreceive the cell ID information indicating whether the cell ID(hereinafter, the second cell ID) used for the (legacy) CRS on theNB-IoT carrier is the same as or different from the first cell ID.

If the second cell ID is the same as the first cell ID, the UE processormay control the UE RF unit to receive the DL signal on the NB-IoTcarrier under the assumption that the CRS is transmitted on the NB-IoTcarrier through the same number of antenna ports as the number ofantenna ports (hereinafter, the NRS ports) used for transmission of anNRS. For example, if the number of NRS ports is 2, the UE processor mayrate-match a corresponding CRS resource location under the assumptionthat the CRS is transmitted from CRS ports 0 and 2. In other words, ifthe number of NRS ports is 2, the UE processor may assume that the CRSis transmitted from CRS ports 0 and 2 and receive or decode the DLsignal under the assumption that there is no corresponding DL signal(e.g., the nPDCCH and/or the nPDSCH) mapped to a corresponding CRSresource location.

If the second cell ID is different from the first cell ID, the UE RFunit may receive the number-of-CRS ports information indicating thenumber of antenna ports (hereinafter, CRS ports) used for transmissionof the CRS. The UE processor may control the UE RF unit to receive theDL signal (e.g., the nPDCCH and/or the nPDSCH) on the NB-IoT carrierunder the assumption that the CRS is transmitted from CRS ports of anumber corresponding to the number-of-CRS ports information.

Upon receiving the CRS on the NB-IoT carrier, the UE processor maycontrol the UE RF unit to receive the DL signal (e.g., the nPDCCH and/orthe nPDSCH) on the NB-IoT carrier under the assumption that the CRS istransmitted at a frequency location (refer to Equation 9 and Equation10) obtained by applying the frequency shift v_(shift) based on thesecond cell ID. The UE processor may control the UE RF unit to receivethe NRS based on the second cell ID.

The UE processor may acquire the carrier information about the NB-IoTcarrier (hereinafter, the data carrier) on a different NB-IoT carrier(hereinafter, an anchor carrier) from the NB-IoT carrier. The carrierinformation may include information indicating a cell ID of the datacarrier. For example, the cell ID may be acquired through the nSSreceived on the anchor carrier. The UE processor may apply the cell IDacquired on the anchor carrier to the data carrier. The data carrier maybe a carrier without the nSS/nPBCH and the anchor carrier may be acarrier with the nSS/nPBCH. The anchor carrier may be a carrieroperating in one PRB within the guard band of the channel band used inthe LTE system.

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to a BS, a UE,or other devices in a wireless communication system.

What is claimed is:
 1. A user equipment for receiving a downlink signalin a narrowband in a wireless communication system, the user equipmentcomprising, at least one transceiver; at least one processor; and atleast one computer memory operably connectable to the at least oneprocessor and storing instructions that, when executed by the at leastone processor, perform operations comprising: acquiring a first cellidentifier through a first carrier; receiving, via the at least onetransceiver, carrier information for a second carrier, wherein thecarrier information includes cell identifier information regardingwhether the same first cell identifier is used in the second carrier;and receiving, via the at least one transceiver, downlink data on thesecond carrier based on the carrier information and a narrowbandreference signal (NB-RS), and wherein each of the first and secondcarriers operates in one resource block (RB), wherein the first carrieris a carrier on which a narrowband synchronization signal (nSS) and anarrowband physical broadcast channel (nPBCH) are present and the secondcarrier is a carrier on which the nSS and the nPBCH are not present, andwherein the NB-RS are received on the second carrier based on the firstcell identifier.
 2. The user equipment according to claim 1, whereinbased on the cell identifier information informing the user equipmentthat the same first cell identifier is used in the second carrier, anumber of antenna ports for a cell specific reference signal (CRS) onthe second carrier is the same as a number of antenna ports for theNB-RS, or wherein based on the cell identifier information not informingthe user equipment that the same first cell identifier is used in thesecond carrier, the carrier information further includesnumber-of-antenna ports information for the CRS.
 3. The user equipmentaccording to claim 2, wherein a frequency location of the CRS isdetermined based on the first cell identifier.
 4. The user equipmentaccording to claim 1, wherein the carrier information further includesinformation regarding a start orthogonal frequency division multiplexing(OFDM) symbol for reception of the downlink data on the second carrier.5. The user equipment according to claim 1, wherein the carrierinformation is received on the first carrier.
 6. The user equipmentaccording to claim 1, wherein the first carrier operates in one RBwithin a guard band of a long term evolution (LTE) system, and thesecond carrier operates in one RB within a channel band of the LTEsystem.
 7. A device for a user equipment in a wireless communicationsystem, the device comprising, at least one processor; and at least onecomputer memory operably connectable to the at least one processor andstoring instructions that, when executed by the at least one processor,perform operations comprising: acquiring a first cell identifier througha first carrier; receiving carrier information for a second carrier,wherein the carrier information includes cell identifier informationregarding whether the same first cell identifier is used in the secondcarrier; and receiving downlink data on the second carrier based on thecarrier information and a narrowband reference signal (NB-RS), andwherein each of the first and second carriers operates in one resourceblock (RB), wherein the first carrier is a carrier on which a narrowbandsynchronization signal (nSS) and a narrowband physical broadcast channel(nPBCH) are present and the second carrier is a carrier on which the nSSand the nPBCH are not present, and wherein the NB-RS are received on thesecond carrier based on the first cell identifier.
 8. The deviceaccording to claim 7, wherein based on the cell identifier informationinforming the user equipment that the same as the same first cellidentifier is used in the second carrier, a number of antenna ports forthe CRS is same as a number of antenna ports for the NB-RS, or whereinbased on the cell identifier information not informing the userequipment that the same first cell identifier is used in the secondcarrier, the carrier information further includes number-of-antennaports information for the CRS.
 9. The device according to claim 8,wherein a frequency location of the CRS is determined based on the firstcell identifier.
 10. The device according to claim 7, wherein thecarrier information further includes information regarding a startorthogonal frequency division multiplexing (OFDM) symbol for receptionof the downlink data on the second carrier.
 11. The device according toclaim 7, wherein the carrier information is received on the firstcarrier.
 12. The device according to claim 7, wherein the first carrieroperates in one RB within a guard band of a long term evolution (LTE)system, and the second carrier operates in one RB within a channel bandof the LTE system.
 13. A base station for transmitting a downlink signalin a narrowband in a wireless communication system, the base stationcomprising, at least one transceiver; at least one processor; and atleast one computer memory operably connectable to the at least oneprocessor and storing instructions that, when executed by the at leastone processor, perform operations comprising: transmitting a first cellidentifier through a first carrier; transmitting, via the at least onetransceiver, carrier information for a second carrier, wherein thecarrier information includes cell identifier information regardingwhether the same first cell identifier is used in the second carrier;and transmitting, via the at least one transceiver, downlink data on thesecond carrier based on the carrier information and a narrowbandreference signal (NB-RS), and wherein each of the first and secondcarriers operates in one resource block (RB), wherein the first carrieris a carrier on which a narrowband synchronization signal (nSS) and anarrowband physical broadcast channel (nPBCH) are present and the secondcarrier is a carrier on which the nSS and the nPBCH are not present, andwherein the NB-RS are transmitted on the second carrier based on thefirst cell identifier.
 14. The base station according to claim 13,wherein based on the cell identifier information informing a userequipment that the same first cell identifier is used in the secondcarrier, a number of antenna ports for a cell specific reference signal(CRS) on the second carrier is same as a number of antenna ports for theNB-RS, or wherein based on the cell identifier information not informingthe user equipment that the same first cell identifier is used on thesecond carrier, the carrier information further includesnumber-of-antenna ports information for the CRS.
 15. The base stationaccording to claim 14, wherein a frequency location of the CRS isdetermined based on the first cell identifier.
 16. The base stationaccording to claim 13, wherein the carrier information further includesinformation regarding a start orthogonal frequency division multiplexing(OFDM) symbol for transmission of the downlink data on the secondcarrier.
 17. The base station according to claim 13, wherein the carrierinformation is transmitted on the first carrier.
 18. The base stationaccording to claim 13, wherein the first carrier operates in one RBwithin a guard band of a long term evolution (LTE) system, and thesecond carrier operates in one RB within a channel band of the LTEsystem.
 19. The user equipment according to claim 1, wherein the cellidentifier information indicates whether a second cell identifier for acell specific reference signal (CRS) on the second carrier is the sameas the first cell identifier.